Publications

131. Evidence for a Nodal Energy Gap in the Iron-Pnictide Superconductor LaFePO from Penetration Depth Measurements by Scanning SQUID Susceptometry,
Clifford W. Hicks, Thomas M. Lippman, Martin E. Huber, James G. Analytis, Jiun-Haw Chu, Ann S. Erickson, Ian R. Fisher, and Kathryn A. Moler,
Phys. Rev. Lett. 103, 127003 (2009).

ABSTRACT
We measure changes in the penetration depth lambda of the Tc ~ 6 K superconductor LaFePO. In the process, scanning SQUID susceptometry is demonstrated as a technique for accurately measuring local temperature-dependent changes in lambda, ideal for studying early or difficult-to-grow materials. Lambda is found to vary linearly with temperatures from 0.36 to 2 K, with a slope of 143 +/- 15 Angstroms/K, suggesting line nodes in the superconducting order parameter. The linear dependence up to ~Tc/3, similar to the cuprate superconductors, indicates well-developed nodes.

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130. Experimental Realization of a Three-Dimensional Topological Insulator, Bi 2Te3,
Y. L. Chen, J. G. Analytis, J.-H. Chu, Z. K. Liu, S.-K. Mo, X. L. Qi, H. J. Zhang, D. H. Lu, X. Dai, Z. Fang, S. C. Zhang, I. R. Fisher, Z. Hussain, Z.-X. ,
Science 325, 178-181 (2009).

ABSTRACT
Three-dimensional topological insulators are a new state of quantum matter with a bulk gap and odd number of relativistic Dirac fermions on the surface. By investigating the surface state of Bi2Te3 with angle-resolved photoemission spectroscopy, we demonstrate that the surface state consists of a single nondegenerate Dirac cone. Furthermore, with appropriate hole doping, the Fermi level can be tuned to intersect only the surface states, indicating a full energy gap for the bulk states. Our results establish that Bi2Te3 is a simple model system for the three-dimensional topological insulator with a single Dirac cone on the surface. The large bulk gap of Bi2Te3 also points to promising potential for high-temperature spintronics applications.

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129. Quantum oscillations in the parent pnictide BaFe2As2: Itinerant electrons in the reconstructed state
James G. Analytis, Ross D. McDonald, Jiun-Haw Chu, Scott C. Riggs, Alimamy F. Bangura, Chris Kucharczyk, Michelle Johannes, and I. R. Fisher,
Phys. Rev. B 80, 064507 (2009).

ABSTRACT
We report quantum-oscillation measurements that enable the direct observation of the Fermi surface of the low-temperature ground state of BaFe2As2. From these measurements we characterize the low-energy excitations, revealing that the Fermi surface is reconstructed in the antiferromagnetic state, but leaving itinerant electrons in its wake. The present measurements are consistent with a conventional band folding picture of the antiferromagnetic ground state, placing important limits on the topology and size of the Fermi surface.

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128. Fermi Surface of SrFe2P2 Determined by the de Haas-van Alphen Effect
J. G. Analytis, C. M. J. Andrew, A. I. Coldea, A. McCollam, J.-H. Chu, R. D. McDonald,I. R. Fisher, and A. Carrington,
Phys. Rev. Lett. 103, 076401, (2009).

ABSTRACT
We report measurements of the Fermi surface (FS) of the ternary iron-phosphide SrFe2P2 using the de Haas-van Alphen effect. The calculated FS of this compound is very similar to SrFe2As2, the parent compound of the high temperature superconductors. Our data show that the Fermi surface is composed of two electron and two hole sheets in agreement with band-structure calculations. Several of the sheets show strong c-axis warping emphasizing the importance of three dimensionality in the nonmagnetic state of the ternary pnictides. We find that the electron and hole pockets have a different topology, implying that this material does not satisfy a (pi,pi) nesting condition.

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127. Evidence for weak electronic correlations in iron pnictides
W. L. Yang, A. P. Sorini, C-C. Chen, B. Moritz, W.-S. Lee, F. Vernay, P. Olalde-Velasco, J. D. Denlinger, B. Delley, J.-H. Chu, J. G. Analytis, I. R. Fisher, Z. A. Ren, J. Yang, W. Lu, Z. X. Zhao, J. van den Brink, Z. Hussain, Z.-X. Shen, and T. P. Devereaux,
Phys. Rev. B 80, 014508, (2009).

ABSTRACT
Using x-ray absorption (XAS) and resonant inelastic x-ray scattering (RIXS), charge dynamics at and near the Fe L edges is investigated in Fe-pnictide materials and contrasted to that measured in other Fe compounds. It is shown that the XAS and RIXS spectra for 122 and 1111 Fe pnictides are each qualitatively similar to Fe metal. Cluster diagonalization, multiplet, and density-functional calculations show that Coulomb correlations are much smaller than in the cuprates, highlighting the role of Fe metallicity and strong covalency in these materials. The best agreement with experiment is obtained using Hubbard parameters U~2 eV and J~0.8 eV.

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126. Electronic structure of the BaFe2As2 family of iron-pnictide superconductors
M. Yi, D. H. Lu, J. G. Analytis, J.-H. Chu, S.-K. Mo, R.-H. He, R. G. Moore, X. J. Zhou, G. F. Chen, J. L. Luo, N. L. Wang, Z. Hussain, D. J. Singh, I. R. Fisher, and Z.-X. Shen,
Phys. Rev. B 80, 024515, (July 24,2009).

ABSTRACT
We use high-resolution angle-resolved photoemission to study the electronic structure of the BaFe2As2 pnictides. We observe two electron bands and two hole bands near the X point,(,) of the Brillouin zone, in the paramagnetic state for electron-doped Ba(Co0.06Fe0.94)2As2, undoped BaFe2As2, and hole-doped Ba0.6K0.4Fe2As2. Among these bands, only the electron bands cross the Fermi level, forming two electron pockets around X while the hole bands approach but never reach the Fermi level. We show that the band structure of the BaFe2As2 family matches reasonably well with the prediction of local-density approximation calculations after a momentum-dependent shift and renormalization. Our finding resolves a number of inconsistencies regarding the electronic structure of pnictides.

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125. Asymmetric Quintuplet Condensation in the Frustrated S = 1 Spin Dimer Compound Ba3Mn2O8
E. C. Samulon, Y. Kohama, R. D. McDonald, M. C. Shapiro, K. A. Al-Hassanieh,C. D. Batista, M. Jaime, and I. R. Fisher,
Phys. Rev. Lett. 103, 047702 (2009).

ABSTRACT
Ba3Mn2O8 is a spin-dimer compound based on pairs of S=1, 3d2, Mn5+ ions arranged on a triangular lattice. Antiferromagnetic intradimer exchange leads to a singlet ground state in zero field, with excited triplet and quintuplet states at higher energy. High field thermodynamic measurements are used to establish the phase diagram, revealing a substantial asymmetry of the quintuplet condensate. This striking effect, all but absent for the triplet condensate, is due to a fundamental asymmetry in quantum fluctuations of the paramagnetic phases near the various critical fields.

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124. Optical properties of the charge density wave rare earth tritelluride compounds: a view on PrTe3,
F. Pfuner, L. DeGiorgi, J.-H. Chu, N. Ru, K. Y. Shin and I. R. Fisher,
Physica B. 404, 533-536 (2009).

ABSTRACT
We report on our recent optical measurements of the Pr tri-telluride charge-density-wave system. Our data, collected over an extremely broad spectral range, allow us to observe both the Drude component and the single-particle peak, ascribed to the contributions due to the free charge carriers and to the charge-density-wave gap excitation, respectively. Our findings perfectly fit within the scenario based on a diminishing impact of the charge-density-wave condensate on the electronic properties upon compressing the lattice, as evinced from our previous investigations on these systems both with chemical as well as with applied pressure.

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123. Topological Change of the Fermi Surface in Ternary Iron Pnictides with Reduced c/a Ratio: A de Haas-van Alphen Study of CaFe2P2 ,
Amalia I. Coldea, C. M. J. Andrew, J. G. Analytis, R. D. McDonald, A. F. Bangura, J.-H. Chu, I. R. Fisher, and A. Carrington,
Phys. Rev. Lett. 103, 026404 (2009).

ABSTRACT
We report a de Haas-van Alphen effect study of the Fermi surface of CaFe2P2 using low-temperature torque magnetometry up to 45 T. This system is a close structural analog of the collapsed tetragonal nonmagnetic phase of CaFe2As2.We find the Fermi surface of CaFe2P2 to differ from other related ternary phosphides in that its topology is highly dispersive in the c axis, being three dimensional in character and with identical mass enhancement on both electron and hole pockets. This suggests that when the bonding between pnictogen layers becomes important nesting conditions are not fulfilled.

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122. Quantum oscillation studies of the Fermi surface of LaFePO,
A. Carrington, A. I. Coldea, J. D. Fletcher, N. E. Hussey, C. M. J. Andrew, A. F. Bangura, J. G. Analytis, J.-H. Chu, A. S. Erickson , I. R. Fisher and R. D. McDonald,
Physica C. 469, 459-468 (2009).

ABSTRACT
We review recent experimental measurements of the Fermi surface of the iron-pnictide superconductor LaFePO using quantum oscillation techniques. These studies show that the Fermi surface topology is close to that predicted by first principles density functional theory calculations, consisting of quasi-twodimensional electron-like and hole-like sheets. The total volume of the two hole sheets is almost equal to that of the two electron sheets, and the hole and electron Fermi surface sheets are close to a nesting condition. No evidence for the predicted three-dimensional pocket arising from the Fe dz2 band is found. Measurements of the effective mass suggest a renormalisation of around two, close to the value for the overall band renormalisation found in recent angle resolved photoemission measurements.

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121. ARPES studies of the electronic structure of LaOFe(P,As),
D. H. Lu, M. Yi, S.-K. Mo, J. G. Analytis, J.-H. Chu, A. S. Erickson, D. J. Singh, Z. Hussain, T. H. Geballe, I. R. Fisher, and Z. X Shen,
Physica C. 469, 452-458 (2009).

ABSTRACT
We report a comparison study of LaOFeP and LaOFeAs, two parent compounds of recently discovered iron-pnictide superconductors, using angle-resolved photoemission spectroscopy. Both systems exhibit some common features that are very different from well-studied cuprates. In addition, important differences have also been observed between these two ferrooxypnictides. For LaOFeP, quantitative agreement can be found between our photoemission data and the LDA band structure calculations, suggesting that a weak coupling approach based on an itinerant ground state may be more appropriate for understanding this new superconducting compound. In contrast, the agreement between LDA calculations and experiments in LaOFeAs is relatively poor, as highlighted by the unexpected Fermi surface topology around (pi,pi). Further investigations are required for a comprehensive understanding of the electronic structure of LaOFeAs and related compounds.

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120. Pressure induced superconducting phase in the charge density wave compound TbTe3,
J. J. Hamlin, D. A. Zocco, T. A. Sayles, M. B. Maple, J. -H. Chu and I. R. Fisher,
Phys. Rev. Lett. 102, 177002 (2009).

ABSTRACT
A series of high-pressure electrical resistivity measurements on single crystals of TbTe3 reveal a complex phase diagram involving the interplay of superconducting, antiferromagnetic and charge-densitywave order. The onset of superconductivity reaches a maximum of almost 4 K (onset) near 12.4 GPa.

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119. Evidence for a Nodal-Line Superconducting State in LaFePO,
J. D. Fletcher, A. Serafin, L. Malone, J. G. Analytis, J.-H. Chu, A. S. Erickson, I. R. Fisher, and A. Carrington,
Phys. Rev. Lett. 102, 147001 (2009).

ABSTRACT
In several iron-arsenide superconductors there is strong evidence for a fully gapped superconducting state consistent with either a conventional s-wave symmetry or an unusual x state where the gap changes sign between the electron and hole Fermi-surface sheets. Here we report measurements of the penetration depth in very clean samples of the related iron-phosphide superconductor, LaFePO, at temperatures down to _100 mK. We find that Lamda varies approximately linearly with T strongly suggesting the presence of gap nodes in this compound. Taken together with other data, this suggests the gap function is not universal for all pnictide superconductors.

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118. Charge dynamics of the spin density wave state in BaFe2As2,
F. Pfuner, J. G. Analytis , J.-H. Chu, I. R. Fisher, and L. Degiorgi,
Eur. Phys. J. B 67, 513-517 (2009).

ABSTRACT
We report on a thorough optical investigation of BaFe2As2 over a broad spectral range and as a function of temperature, focusing our attention on its spin-density-wave (SDW) phase transition at TSDW = 135 K. While BaFe2As2 remains metallic at all temperatures, we observe a depletion in the far infrared energy interval of the optical conductivity below TSDW, ascribed to the formation of a pseudogaplike feature in the excitation spectrum. This is accompanied by the narrowing of the Drude term consistent with the dc transport results and suggestive of suppression of scattering channels in the SDW state. About 20% of the spectral weight in the far infrared energy interval is affected by the SDW phase transition.

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117. Pressure-induced quenching of the charge-density-wave state in rare-earth tritellurides observed by x-ray diffraction,
A. Sacchetti, C. L. Condron, S. N. Gvasaliya, F. Pfuner, M. Lavagnini, M. Baldini, M. F. Toney, M. Merlini, M. Hanfland, J. Mesot, J.-H. Chu, I. R. Fisher, P. Postorino, and L. Degiorgi,
Phys. Rev. B. 79, 201101(R) (2009).

ABSTRACT
We report an x-ray diffraction study on the charge-density-wave LaTe3 and CeTe3 compounds as a function of pressure. We extract the lattice constants and the CDW modulation wave vector. We observe that the intensity of the CDW satellite peaks tend to zero with increasing pressure, thus providing direct evidence for a pressure-induced quenching of the CDW phase. Our findings further support the equivalence between chemical and applied pressures in RTe3, put forward by our previous optical investigations, but reveal some subtle differences. We offer a possible explanation for these differences.

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116. Neutron scattering study of the interplay between structure and magnetism in Ba(Fe_{1-x}Co_{x})2As2 ,
C. Lester, Jiun-Haw Chu, J. G. Analytis, S. C. Capelli, A. S. Erickson, C. L. Condron, M. F. Toney, I. R. Fisher and S. M. Hayden,
Phys. Rev. B. 79, 144523 (2009).

ABSTRACT
Single-crystal neutron diffraction is used to investigate the magnetic and structural phase diagrams of the electron-doped superconductor Ba(Fe_{1-x}Co_{x})2As2. Heat-capacity and resistivity measurements have demonstrated that Co doping this system splits the combined antiferromagnetic and structural transition present in BaFe2As2 into two distinct transitions. For x=0.025, we find that the upper transition is between the hightemperature tetragonal and low-temperature orthorhombic structures with T_{to}=99+/-0.5K and the antiferromagnetic transition occurs at T_{AF}=93+/-O.5K We find that doping rapidly suppresses the antiferromagnetism, with antiferromagnetic order disappearing at x0.055. However, there is a region of coexistence of antiferromagnetism and signatures of superconductivity obtained from thermodynamic and transport properties. For all the compositions studied, we find two anomalies in the temperature dependence of the structural Bragg peaks from both neutron scattering and x-ray diffraction at the same temperatures where anomalies in the heat capacity and resistivity have been previously identified. Thus for x=0.025, where we have shown that the lower anomaly occurs at TAF, we infer that there is strong coupling between the antiferromagnetism and the crystal lattice which may persist to larger x.

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115. High pressure transport and thermodynamic properties of CeTe3,
D. A. Zocco, J. J. Hamlin, T. A. Sayles, M. B. Maple, J. -H. Chu and I. R. Fisher ,
Phys. Rev. B. 79, 134428 (2009).

ABSTRACT
We have performed high-pressure, electrical resistivity, and specific heat measurements on CeTe3 single crystals. Two magnetic phases with nonparallel magnetic easy axes were detected in electrical resistivity and specific heat at low temperatures. We also observed the emergence of an additional phase at high pressures and low temperatures and a possible structural phase transition detected at room temperature and at 45 kbar, which can possibly be related with the lowering of the charge-density wave transition temperature known for this compound.

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114. Fine Structure in the Electronic Density of States near the Fermi Energy of Al-Ni-Co Decagonal Quasicrystal from Ultrafast Time-Resolved Optical Reflectivity,
T. Mertelj, A. Olak, J. Dolinek, I. R. Fisher, V. V. Kabanov and D. Mihailovic,
Phys. Rev. Lett. 102, 086405 (2009).

ABSTRACT
We measured the temperature and fluence dependence of the time-resolved photoinduced optical reflectivity in a decagonal Al71.9Ni11.1Co17.0 quasicrystal. We find no evidence for the relaxation of a hot thermalized electron gas as observed in metals. Instead, a quick diffusion of the hot nonthermal carriers 40 nm into the bulk is detected, enhanced by the presence of a broad pseudogap. From the relaxation dynamics we find evidence for the suppression of the electronic density of states (DOS) at the Fermi energy with respect to the electronic DOS at 13 meV away from the Fermi energy which is consistent with recent theoretical calculations.

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113. Pressure dependence of the single particle excitation in the charge-density-wave CeTe3 system,
M. Lavagnini, A. Sacchetti, C. Marini, M. Valentini, R. Sopracase, A. Perucchi, P. Postorino, S. Lupi, J.-H. Chu, I. R. Fisher, and L. Degiorgi,
Phys. Rev. B, 79, 075117 (2009).

ABSTRACT
We present data on the pressure dependence at 300 K of the optical reflectivity of CeTe3, which undergoes a charge-density-wave phase transition well above room temperature. The collected data cover an unprecedented broad spectral range from the infrared up to the ultraviolet, which allows a robust determination of the gap as well as of the fraction of the Fermi surface affected by the formation of the CDW condensate. Upon compressing the lattice there is a progressive closing of the gap, inducing a transfer of spectral weight from the gap feature into the Drude component. At frequencies above the CDW gap we also identify a power-law behavior, consistent with findings along the RTe3 series (i.e., chemical pressure) and suggestive of a Tomonaga-Luttinger liquid scenario at high-energy scales. This set of data is placed in the context of our previous investigations of this class of materials and allows us to revisit important concepts for the physics of CDW state in layeredlike two-dimensional systems.

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112. Enhanced superconducting pairing interaction in indium-doped tin telluride,
A. S. Erickson, J. -H. Chu, M. F. Toney, T. H. Geballe and I. R. Fisher,
Phys. Rev. B, 79, 024520 (2009).

ABSTRACT
The ferroelectric degenerate semiconductor Sn_{1-delta}Te exhibits superconductivity with critical temperatures, Tc, of up to 0.3 K for hole densities of order 10^21 cm^3. When doped on the tin site with greater than xc 1.7(3)% indium atoms, however, superconductivity is observed up to 2 K, though the carrier density does not change significantly. We present specific-heat data showing that a stronger pairing interaction is present for x>xc than for x
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111. Determination of the phase diagram of the electron doped superconductor Ba(Fe_{1-x}Co_{x})2As2,
J.-H. Chu, J. G. Analytis, C. Kucharczyk & I. R.Fisher,
Phys. Rev. B, 79, 014506 (2009).

ABSTRACT
Systematic measurements of the resistivity, heat capacity, susceptibility, and Hall coefficient are presented for single-crystal samples of the electron-doped superconductor Ba(Fe_{1-x}Co_{x})2As2. These data delineate an x-T phase diagram in which the single magnetic/structural phase transition that is observed for undoped BaFe2As2 at 134 K appears to split into two distinct phase transitions, both of which are rapidly suppressed with increasing Co concentration. Superconductivity emerges for Co concentrations above x=0.025 and appears to coexist with the broken-symmetry state for an appreciable range of doping up to x=0.06. The optimal superconducting transition temperature appears to coincide with the Co concentration at which the magnetic/ structural phase transitions are totally suppressed, at least within the resolution provided by the finite-step size between crystals prepared with different doping levels. Superconductivity is observed for a further range of Co concentrations before being completely suppressed for x=0.18 and above. The form of this x-T phase diagram is suggestive of an association between superconductivity and a quantum critical point arising from suppression of the magnetic and/or structural phase transitions.

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110. Single-particle and collective mode couplings associated with 1- and 2-directional electronic ordering in metallic RTe_3 (R = Ho, Dy, Tb)
R. V. Yusupov, T. Mertelj, J.-H. Chu, I. R. Fisher and D. Mihailovic,
Phys. Rev. Lett. 101, 246402 (2008).

ABSTRACT
The coupling of phonons with collective modes and single-particle gap excitations associated with one- (1d) and two-directional (2d) electronically driven charge-density wave (CDW) ordering in metallic RTe3 is investigated as a function of rare-earth ion chemical pressure (R = Tb; Dy; Ho) using femtosecond pump-probe spectroscopy. From the T dependence of the CDW gap delta_CDW and the amplitude mode, we find that while the transition to a 1d-CDWordered state at Tc1 initially proceeds in an exemplary meanfield- like fashion, below Tc1, delta_CDW is depressed and departs from the mean-field behavior. The effect is apparently triggered by resonant mode mixing of the amplitude mode with a totally symmetric phonon at 1.75 THz. At low temperatures, when the state evolves into a 2d-CDWordered state at Tc2 in the DyTe3 and HoTe3, additional much weaker mode mixing is evident but no soft mode is observed.

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109. Fermi Surface of Superconducting LaFePO Determined from Quantum Oscillations
A.I. Coldea, J.D. Fletcher, A. Carrington, J.G. Analytis, A.F. Bangura, J.-H. Chu, A.S. Erickson, I.R. Fisher, N.E. Hussey, R.D. McDonald,
Phys. Rev. Lett. 101, 216402 (2008).

ABSTRACT
We report extensive measurements of quantum oscillations in the normal state of the Fe-based superconductor LaFePO, (Tc~6 K) using low temperature torque magnetometry and transport in high static magnetic fields (45 T). We find that the Fermi surface is in broad agreement with the band-structure calculations with the quasiparticle mass enhanced by a factor ~2. The quasi-two-dimensional Fermi surface consists of nearly nested electron and hole pockets, suggesting proximity to a spin or charge density wave instability.

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108. Evidence for coupling between charge density waves and phonons in two-dimensional rare earth tellurides
M. Lavagnini, M. Baldini, A. Sacchetti, D. Di Castro, B. Delley, R. Monnier, J.-H. Chu, N. Ru, I.R. Fisher, P. Postorino and L. Degiorgi,
Phys. Rev. B 78, 201101(R) (2008).

ABSTRACT
We report on a Raman-scattering investigation of the charge density wave (CDW) quasi-two-dimensional rare-earth tritellurides RTe3 (R=La, Ce, Pr, Nd, Sm, Gd, and Dy) at ambient pressure, and of LaTe3 and CeTe3 under externally applied pressure. The observed phonon peaks can be ascribed to the Raman-active modes for both the undistorted and the distorted lattices in the CDW state by means of a first-principles calculation. The latter also predicts the Kohn anomaly in the phonon dispersion, driving the CDW transition. The integrated intensity of the two most prominent modes scales as a characteristic power of the CDW-gap amplitude upon compressing the lattice, which provides clear evidence for the tight coupling between the CDW condensate and the vibrational modes.

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107. Transient Electronic Structure and Melting of a Charge Density Wave in TbTe3
F. Schmitt, P. S. Kirchmann, U. Bovensiepen, R. G. Moore, L. Rettig, M. Krenz, J.-H. Chu, N. Ru, L. Perfetti, D. H. Lu, M. Wolf, I. R. Fisher and Z.-X. Shen,
Science 321, 1649-1652 (2008).

ABSTRACT
Obtaining insight into microscopic cooperative effects is a fascinating topic in condensed matter research because, through self-coordination and collectivity, they can lead to instabilities with macroscopic impacts like phase transitions. We used femtosecond time- and angle-resolved photoelectron spectroscopy (trARPES) to optically pump and probe TbTe3, an excellent model system with which to study these effects. We drove a transient charge density wave melting, excited collective vibrations in TbTe3, and observed them through their time-, frequency-, and momentum-dependent influence on the electronic structure. We were able to identify the role of the observed collective vibration in the transition and to document the transition in real time. The information that we demonstrate as being accessible with trARPES will greatly enhance the understanding of all materials exhibiting collective phenomena.

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106. Electronic structure of the iron-based superconductor LaOFeP
D. H. Lu, M. Yi, S.-K. Mo, A. S. Erickson, J. Analytis, J.-H. Chu, D. J. Singh, Z. Hussain, T. H. Geballe, I. R. Fisher & Z.-X. Shen,
Nature 455, 81-84 (2008).

ABSTRACT
The recent discovery of superconductivity in the iron oxypnictide family of compounds has generated intense interest. The layered crystal structure with transition-metal ions in planar square-lattice form and the discovery of spin-density-wave order near 130 K seem to hint at a strong similarity with the copper oxide superconductors. An important current issue is the nature of the ground state of the parent compounds. Two distinct classes of theories, distinguished by the underlying band structure, have been put forward: a local-moment antiferromagnetic ground state in the strong-coupling approach, and an itinerant ground state in the weak-coupling approach. The first approach stresses onsite correlations, proximity to a Mott-insulating state and, thus, the resemblance to the high-transition-temperature copper oxides, whereas the second approach emphasizes the itinerant-electron physics and the interplay between the competing ferromagnetic and antiferromagnetic fluctuations. The debate over the two approaches is partly due to the lack of conclusive experimental information on the electronic structures. Here we report angle-resolved photoemission spectroscopy (ARPES) of LaOFeP (superconducting transition temperature, Tc=5.9 K), the first-reported iron-based superconductor. Our results favour the itinerant ground state, albeit with band renormalization. In addition, our data reveal important differences between these and copper-based superconductors.

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105. De Haas-van Alphen oscillations in the charge-density wave compound lanthanum tritelluride (LaTe3)
N. Ru, R. A. Borzi, A. Rost , A. P. Mackenzie , J. Laverock, S.B. Dugdale, and I. R. Fisher,
Phys. Rev. B 78, 045123 (2008).

ABSTRACT
de Haas–van Alphen oscillations were measured in lanthanum tritelluride (LaTe3) to probe the partially gapped Fermi surface (FS) resulting from charge density wave (CDW) formation. Three distinct frequencies were observed, one of which can be correlated with a FS sheet that is unaltered by CDW formation. The other two frequencies arise from FS sheets that have been reconstructed in the CDW state. All three pockets are quasi-two-dimensional, consistent with expectations from band-structure calculations. Analysis of the field dependence of the oscillations is used to provide an estimate of the geometry of the reconstructed FS sections.

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104. Magnetic properties of the charge density wave compounds RTe3, R=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er & Tm
N. Ru, J.-H. Chu and I. R. Fisher,
Phys. Rev. B 78, 012410 (2008).

ABSTRACT
The antiferromagnetic transition is investigated in the rare-earth (R) tritelluride RTe3 family of charge-density wave (CDW) compounds via specific heat, magnetization, and resistivity measurements. Observation of the opening of a superzone gap in the resistivity of DyTe3 indicates that additional nesting of the reconstructed Fermi surface in the CDW state plays an important role in determining the magnetic structure.

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103. Ordered magnetic phases of the frustrated spin-dimer compound Ba3Mn2O8
E. C. Samulon, Y.-J. Jo, P. Sengupta, C. D. Batista, M. Jaime, L. Balicas and I. R. Fisher,
Phys. Rev. B 77, 214441 (2008).

ABSTRACT
Ba3Mn2O8 is a spin-dimer compound based on pairs of S=1, 3d2, Mn5+ ions arranged on a triangular lattice. Antiferromagnetic intradimer exchange leads to a singlet ground state in zero field. Here we present the first results of thermodynamic measurements for single crystals probing the high-field ordered states of this material associated with closing the spin gap to the excited triplet states. Specific heat, magnetocaloric effect, and torque magnetometry measurements were performed in magnetic fields up to 32 T and temperatures down to 20 mK. For fields above Hc1~8.7 T, these measurements reveal a single magnetic phase for H parallel c but two distinct phases (approximately symmetric about the center of the phase diagram) for H perpendicular to c. Analysis of the simplest possible spin Hamiltonian describing this system yields candidates for these ordered states corresponding to a simple spiral structure for H parallel to c and to two distinct modulated phases for H perpendicular to c. Both single-ion anisotropy and geometric frustration play crucial roles in defining the phase diagram.

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102. Singlet-Triplet Dispersion Reveals Additional Frustration in the Triangular-Lattice Dimer Compound Ba3Mn2O8
M. B. Stone, M. D. Lumsden, S. Chang, E. C. Samulon, C. D. Batista, and I. R. Fisher,
Phys. Rev. Lett 100, 237201 (2008).

ABSTRACT
We present single crystal inelastic neutron scattering measurements of the S=1 dimerized quasi-two-dimensional antiferromagnet Ba3Mn2O8. The singlet-triplet dispersion reveals nearest-neighbor and next-nearest-neighbor ferromagnetic interactions between adjacent bilayers that compete against each other. Although the interbilayer exchange is comparable to the intrabilayer exchange, this additional frustration reduces the effective coupling along the c axis and leads to a quasi-two-dimensional behavior. In addition, the obtained exchange values are able to reproduce the four critical fields in the phase diagram.

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101. Optical properties of the charge-density-wave polychalcogenide compounds R2Te5 (R=Nd, Sm and Gd)
F. Pfuner, L. Degiorgi, K.Y. Shin and I. R. Fisher,
Eur. Phys. J. B 63, 11–16 (2008).

ABSTRACT
We investigate the rare-earth polychalcogenide R2Te5 (R=Nd, Sm and Gd) charge-density wave (CDW) compounds by optical reflectivity measurements. We obtain the optical conductivity through Kramers-Kronig transformation of the reflectivity spectra. From the real part of the optical conductivity we then extract the excitation energy of the CDW gap and estimate the fraction of the Fermi surface which is gapped by the formation of the CDW condensate. In analogy to previous findings on the related RTen (n = 2 and 3) families, we establish the progressive closing of the CDW gap and the moderate enhancement of the metallic component upon chemically compressing the lattice.

Link to full article.

100. Angle-resolved photoemission study of the evolution of band structure and charge density wave properties in RTe3 ( R=Y , La, Ce, Sm, Gd, Tb, and Dy)
V. Brouet, W. L. Yang, X. J. Zhou, Z. Hussain, R. G. Moore, R. He, D. H. Lu, Z. X. Shen, J. Laverock, S. B. Dugdale, N. Ru, and I. R. Fisher,
Phys. Rev. B 77, 235104 (2008).

ABSTRACT
We present a detailed angle-resolved photoemission spectroscopy (ARPES) investigation of the RTe3 family, which sets this system as an ideal “textbook” example for the formation of a nesting driven charge density wave (CDW). This family indeed exhibits the full range of phenomena that can be associated to CDW instabilities, from the opening of large gaps on the best nested parts of Fermi surface (up to 0.4 eV), to the existence of residual metallic pockets. ARPES is the best suited technique to characterize these features, thanks to its unique ability to resolve the electronic structure in k space. An additional advantage of RTe3 is that the band structure can be very accurately described by a simple two dimensional tight-binding (TB) model, which allows one to understand and easily reproduce many characteristics of the CDW. In this paper, we first establish the main features of the electronic structure by comparing our ARPES measurements with the linear muffin-tin orbital band calculations. We use this to define the validity and limits of the TB model. We then present a complete description of the CDW properties and of their strong evolution as a function of R. Using simple models, we are able to reproduce perfectly the evolution of gaps in k space, the evolution of the CDW wave vector with R, and the shape of the residual metallic pockets. Finally, we give an estimation of the CDW interaction parameters and find that the change in the electronic density of states n(EF), due to lattice expansion when different R ions are inserted, has the correct order of magnitude to explain the evolution of the CDW properties.

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99. Dispersive magnetic excitations in the S = 1 antiferromagnet Ba3Mn2O8
M. B. Stone, M. D. Lumsden, Y. Qiu, E. C. Samulon, C. D. Batista and I. R. Fisher,
Phys. Rev. B 77, 134406 (2008).

ABSTRACT
We present powder inelastic neutron scattering measurements of the S=1 dimerized antiferromagnet Ba3Mn2O8. The T = 1.4 K magnetic spectrum exhibits a spin gap of 1.0 meV and a dispersive spectrum with a bandwidth of approximately 1.5 meV. A comparison to coupled dimer models accurately describes the dispersion and scattering intensity and determines the exchange constants in Ba3Mn2O8. The wave vector dependent scattering intensity confirms the proposed S=1 dimer bond. Temperature dependent measurements of the magnetic excitations indicate the presence of both singlet-triplet and thermally activated triplet-quintet excitations.

Link to full article.

98. Pressure dependence of the optical properties of the charge-density-wave compound LaTe2
M. Lavagnini, A. Sacchetti, L. Degiorgi, E. Arcangeletti, L. Baldassarre, P. Postorino, S. Lupi, A. Perucchi, K. Y. Shin and I. R. Fisher,
Phys. Rev. B 77, 165132 (2008).

ABSTRACT
We report the pressure dependence of the optical response of LaTe2, which is deep in the charge-density-wave (CDW) ground state even at 300 K. The reflectivity spectrum is collected in the midinfrared spectral range at room temperature and at pressures between 0 and 7 GPa. We extract the energy scale due to the single-particle excitation across the CDW gap and the Drude weight. We establish that the gap decreases upon compressing the lattice while the Drude weight increases. This signals a reduction in the quality of nesting upon applying pressure, therefore inducing a lesser impact of the CDW condensate on the electronic properties of LaTe2. The consequent suppression of the CDW gap leads to a release of additional charge carriers, manifested by the shift of weight from the gap feature into the metallic component of the optical response. On the contrary, the power-law behavior, seen in the optical conductivity at energies above the gap excitation and indicating a weakly interacting limit within the Tomonaga-Luttinger liquid scenario, seems to be only moderately dependent on pressure.

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97. Charge density wave formation in R2Te5 (R = Nd, Sm, Gd)
K. Y. Shin, J. Laverock, Y. Q. Wu, C. L. Condron, M.F. Toney, S. B. Dugdale, M. J. Kramer and I. R. Fisher,
Phys. Rev. B 77, 165101 (2008).

ABSTRACT
The rare earth (R) tellurides R2Te5 have a crystal structure intermediate between that of RTe2 and RTe3, consisting of alternating single and double Te planes sandwiched between RTe block layers. We have successfully grown single crystals of Nd2Te5, Sm2Te5, and Gd2Te5 from a self-flux and we describe here evidence for charge density wave formation in these materials. The superlattice patterns for all three compounds are relatively complex, consisting at room temperature of at least two independent wave vectors. Consideration of the electronic structure indicates that, to a large extent, these wave vectors are separately associated with sheets of the Fermi surface which are principally derived from the single and double Te layers.

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96. Effect of chemical pressure on the charge density wave transition in rare-earth tritellurides RTe3
N. Ru, C. L. Condron, G. Y. Margulis, K. Y. Shin, J. Laverock, S. B. Dugdale, M. F. Toney, and I. R. Fisher,
Phys. Rev. B 77, 035114 (2008).

ABSTRACT
The charge density wave transition is investigated in the bilayer family of rare-earth tritelluride RTe3 compounds (R=Sm, Gd, Tb, Dy, Ho, Er, and Tm) via high-resolution x-ray diffraction and electrical resistivity. The transition temperature increases monotonically with increasing lattice parameter from 244(3) K for TmTe3 to 416(3) K for SmTe3. The heaviest members of the series, R=Dy, Ho, Er, and Tm, are observed to have a second transition at a lower temperature, which marks the onset of an additional charge density wave with wave vector almost equal in magnitude to the first, but oriented in the perpendicular direction.

Link to full article.
Erratum.

95. Reply to Comment on “Extrinsic origin of the insulating behavior of polygrain icosahedral Al-Pd-Re quasicrystals”
J. Dolinsek, P. J. McGuiness, M. Klanjsek, I. Smiljanic, A. Smontara, E. S. Zijlstra, S. K. Bose, I. R. Fisher, M. J. Kramer and P. C. Canfield,
Phys. Rev. B 76, 216202 (2007).

ABSTRACT
We clarify issues raised in the preceding Comment regarding the viewpoint that the highly porous and oxidized arc-melted polygrain i-Al-Pd-Re samples could reveal intrinsic electrical transport properties of this icosahedral family. Flux-grown single-grain i-Al-Pd-Re samples of superior structural quality do not show insulatinglike behavior, and their transport properties are on common ground with all other Al-based icosahedral families.

Link to full article.

94. Nuclear magnetic resonance evidence for a strong modulation of the Bose-Einstein condensate in BaCuSi2O6
S. Krämer R. Stern, M. Horvatic, C. Berthier, T. Kimura, and I. R. Fisher
Phys. Rev. B 76, 100406(R) (2007).

ABSTRACT
We present a 63,65Cu and 29Si NMR study of the quasi-2D coupled spin 1/2 dimer compound BaCuSi2O6 in the magnetic field range 13–26 T and at temperatures as low as 50 mK. NMR data in the gapped phase reveal that below 90 K different intradimer exchange couplings and different gaps (B/A=1.16) exist in every second plane along the c axis, in addition to a planar incommensurate (IC) modulation. 29Si spectra in the field induced magnetic ordered phase reveal that close to the quantum critical point at Hc1=23.35 T the average boson density of the Bose-Einstein condensate is strongly modulated along the c axis with a density ratio for every second plane A/B5. An IC modulation of the local density is also present in each plane.

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93. STM Studies of TbTe3: Evidence for a Fully Incommensurate Charge Density Wave
A. Fang, N. Ru, I. R. Fisher and A. Kapitulnik
Phys. Rev. Lett 99, 046401 (2007).

ABSTRACT
We observe unidirectional charge density wave (CDW) ordering on the quasi-2D material TbTe3 with a scanning tunneling microscope at ~6 K. Our analysis indicates that the CDW is fully incommensurate, with wave vector q_CDW ~ 0.71×2pi/c. By imaging at various tip-sample voltages, we highlight effects of the subsurface layer and its effect on the CDW. We also observe an additional (possibly surface) dimerization and 0.68×2pi/a ordering perpendicular to the CDW.

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92. Ferromagnetism in the Mott Insulator Ba2NaOsO6
A. S. Erickson, S. Misra, G. J. Miller, R. R. Gupta, Z. Schlesinger, W. A. Harrison, J. M. Kim, and I. R. Fisher
Phys. Rev. Lett 99, 016404 (2007).

ABSTRACT
Results are presented of single crystal structural, thermodynamic, and reflectivity measurements of the double-perovskite Ba2NaOsO6. These characterize the material as a 5d1 ferromagnetic Mott insulator with an ordered moment of ~0.2µ_B per formula unit and T_C=6.8(3) K. The magnetic entropy associated with this phase transition is close to Rln2, indicating that the quartet ground state anticipated from consideration of the crystal structure is split, consistent with a scenario in which the ferromagnetism is associated with orbital ordering.

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91. Geometric frustration and dimensional reduction at a quantum critical point
C. D. Batista, J. Schmalian, N. Kawashima, P. Sengupta, S. E. Sebastian, N. Harrison, M. Jaime and I. R. Fisher
Phys. Rev. Lett 98, 257201 (2007).

ABSTRACT
We show that the spatial dimensionality of the quantum critical point associated with Bose-Einstein condensation at T=0 is reduced when the underlying lattice comprises layers coupled by a frustrating interaction. Our theoretical predictions for the critical behavior correspond very well with recent measurements in BaCuSi2O6 [ S. E. Sebastian et al., Nature (London) 441, 617 (2006)].

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90. Optical properties of the Ce and La ditelluride charge density wave compounds
M. Lavagnini, A. Sacchetti, L. DeGiorgi, K. Y. Shin and I. R. Fisher
Phys. Rev. B 75, 205133 (2007).

ABSTRACT
The La and Ce ditellurides LaTe2 and CeTe2 are deep in the charge-density-wave (CDW) ground state even at 300 K. We have collected their electrodynamic response over a broad spectral range from the far infrared up to the ultraviolet. We establish the energy scale of the single particle excitation across the CDW gap. Moreover, we find that the CDW collective state gaps a large portion of the Fermi surface. Based on the observation of a power-law behavior in the optical conductivity, similar to that found for the related rare-earth tritellurides but over a reduced frequency range, we suggest that interactions and umklapp processes may play a role in the onset of the CDW broken-symmetry ground state.

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89. Pressure Dependence of the Charge-Density-Wave Gap in Rare-Earth Tritellurides
A. Sacchetti, E. Arcangeletti, A. Perucchi, L. Baldassarre, P. Postorino, S. Lupi, N. Ru, I. R. Fisher and L. Degiorgi
Phys. Rev. Lett. 98, 026401 (2007).

ABSTRACT
We investigate the pressure dependence of the optical properties of CeTe3, which exhibits an incommensurate charge-density-wave (CDW) state already at 300 K. Our data are collected in the midinfrared spectral range at room temperature and at pressures between 0 and 9 GPa. The energy for the single particle excitation across the CDW gap decreases upon increasing the applied pressure, similarly to the chemical pressure by rare-earth substitution. The broadening of the bands upon lattice compression removes the perfect nesting condition of the Fermi surface and therefore diminishes the impact of the CDW transition on the electronic properties of RTe3.

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88. Multiple Magnon Modes and Consequences for the Bose-Einstein Condensed Phase in BaCuSi2O6
Ch. Rüegg, D. F. McMorrow, B. Normand, H. M. Ronnow, S. E. Sebastian, I. R. Fisher, C. D. Batista, S. Gvasaliya, Ch. Niedermayer, J. Stahn
Phys. Rev. Lett. 98, 017202 (2007).

ABSTRACT
The compound BaCuSi2O6 is a quantum magnet with antiferromagnetic dimers of S=1/2 moments on a quasi-2D square lattice. We have investigated its spin dynamics by inelastic neutron scattering experiments on single crystals with an energy resolution considerably higher than in an earlier study. We observe multiple magnon modes, indicating clearly the presence of magnetically inequivalent dimer sites. The more complex spin Hamiltonian revealed in our study leads to a distinct form of magnon Bose-Einstein condensate phase with a spatially modulated condensate amplitude.

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87. Bose-Einstein condensation in BaCuSi2O6
N. Harrison, S. E. Sebastian, C. D. Batista, M. Jaime, L. Balicas, P. A. Sharma, N. Kawashima and I. R. Fisher
J. Phys.: Conf. Ser. 51, 9-14 (2006).

ABSTRACT
BaCuSi2O6 is a model spin dimer system in which a BEC QCP is realised. Universal BEC power law scaling is experimentally observed, with 3d critical behaviour above 0.5 K, but a crossover to 2d BEC critical scaling down to 30 mK. Here we briefly review and expand on the results presented in the recent Nature paper.

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86. Role of anisotropy in the spin-dimer compound BaCuSi2O6
S. E. Sebastian, P. Tanedo, P. A. Goddard, S.-C. Lee, A. Wilson, S. Kim, S. Cox, R. D. McDonald, S. Hill, N. Harrison, C. D. Batista and I. R. Fisher
Phys. Rev. B. 74, 180401(R) (2006).

ABSTRACT
We present results of magnetization and electron paramagnetic resonance experiments on the spin dimer system BaCuSi2O6. Evidence indicates that the origin of anisotropic terms in the spin Hamiltonian lies in magnetic dipolar interactions. Axial symmetry breaking is on a very small energy scale of < 11 mK, confirming Bose Einstein condensation critical scaling over an extended temperature range in the vicinity of the quantum critical point.

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85. Type II superconducting parameters of Tl-doped PbTe determined from heat capacity and electronic transport measurements
Y. Matsushita, P. Wianicki, A. T. Sommer, T. H. Geballe and I. R. Fisher
Phys. Rev. B. 74, 134512 (2006).

ABSTRACT
Tl-doped PbTe (Pb_{1-x}Tl_{x}Te) is an anomalous superconductor with a remarkably high maximum T_c value given its relatively low carrier concentration. Here, we present results of systematic measurements of superconducting parameters for this material, for Tl concentrations up to x=1.4%. We find that it is a Type II, weak-coupled BCS superconductor in the dirty limit and discuss implications for the applicability of the charge Kondo model recently proposed to account for superconductivity in this system.

Link to full article.

84. Extrinsic origin of the insulating behavior of polygrain icosahedral Al-Pd-Re quasicrystals
J. Dolinsek, P. J. McGuiness, M. Klanjsek, I. Smiljanic, A. Smontara, E. S. Zijlstra, S. K. Bose, I. R. Fisher, M. J. Kramer and P. C. Canfield
Phys. Rev. B. 74, 134201 (2006).

ABSTRACT
Polygrain icosahedral i-Al-Pd-Re quasicrystals are known to exhibit dramatically different electronic transport properties to other Al-based quasicrystals. By performing comparative experimental and theoretical studies of the electronic transport and electronic structure of polygrain and monocrystalline i-Al-Pd-Re samples, we show that the extraordinarily high electrical resistivity and the metal-to-insulator transition in the polygrain material are not intrinsic properties of the quasiperiodic lattice, but are of extrinsic origin due to the high porosity and the oxygen-rich weakly insulating regions in the material. We also compare theoretical electronic structures and experimental electrical resistivities of monocrystalline i-Al-Pd-Re and i-Al-Pd-Mn quasicrystals and show that there are no significant differences between these two isomorphous compounds, suggesting that i-Al-Pd-Re is on common ground with other Al-based quasicrystals. We present a structural model of i-Al-Pd-Re.

Link to full article.

83. Chemical pressure and hidden one-dimensional behavior in rare earth tri-telluride charge density wave compounds
A. Sacchetti, L. Degiorgi, T. Giamarchi, N. Ru and I. R. Fisher,
Phys. Rev. B. 74, 125115 (2006).

ABSTRACT
We report on the first optical measurements of the rare-earth tri-telluride charge-density wave systems. Our data, collected over an extremely broad spectral range, allow us to observe both the Drude component and the single-particle peak, ascribed to the contributions due to the free charge carriers and to the charge-density wave gap excitation, respectively. The data analysis displays a diminishing impact of the charge-density wave condensate on the electronic properties with decreasing lattice constant across the rare-earth series. We propose a possible mechanism describing this behavior and we suggest the presence of a one-dimensional character in these two-dimensional compounds. We also envisage that interactions and umklapp processes might play a relevant role in the formation of the charge-density wave state in these compounds.

Link to full article.

82. Comment on “Bose-Einstein condensation of magnons in Cs2CuCl4”
S. E. Sebastian, V. S. Zapf, N. Harrison, C. D. Batista, P. A. Sharma, M. Jaime, I. R. Fisher and A. Lacerda
Phys. Rev. Lett. 96, 189703 (2006).


 Link to full article.

81. Use of periodic approximants in a dynamical LEED study of the quasicrystalline tenfold surface of decagonal Al-Ni-Co
K. Pussi, N. Ferralis, M. Mihalkovic, M. Widom, S. Curtarolo, M. Gierer, C. J. Jenks, P. C. Canfield, I. R. Fisher and R. D. Diehl
Phys. Rev. B. 73, 184203 (2006).

ABSTRACT
The determination of quasicrystal (QC) surface structures is a challenge to current surface structure techniques. Low-energy electron diffraction (LEED) is the primary technique for the determination of periodic surface structures, but application of dynamical LEED to quasicrystals requires the use of many approximations. In this study, two different approaches were used to apply dynamical LEED to the structure of the tenfold surface of decagonal Al73Ni10Co17. One method (method 1) involves the use of a quasicrystalline model along with approximations that average over the composition and local geometries. The other method (method 2) uses periodic models that approximate the actual local QC structure (approximants) in more exact, atomistic calculations. Although the results using the two methods were consistent, the results of the approximant analysis (method 2) suggested a different way to apply the approximations in method 1, resulting in a better fit between experimental and calculated beams. Thus, periodic approximant structure models can provide a simpler and more efficient method for the determination of local geometries in QC surfaces, and may also facilitate analyses using quasicrystal models.

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80. Dimensional reduction at a quantum critical point
S. E. Sebastian, N. Harrison, C. D. Batista, L. Balicas, M. Jaime, P. A. Sharma, N. Kawashima and I. R. Fisher
Nature vol. 441, number 7093, pp 617-620 (June 1st 2006).

ABSTRACT
Competition between electronic ground states near a quantum critical point (QCP) — the location of a zero-temperature phase transition driven solely by quantum-mechanical fluctuations — is expected to lead to unconventional behaviour in low-dimensional systems. New electronic phases of matter have been predicted to occur in the vicinity of a QCP by two-dimensional theories, and explanations based on these ideas have been proposed for signifi- cant unsolved problems in condensed-matter physics, such as non-Fermi-liquid behaviour and high-temperature superconductivity. But the real materials to which these ideas have been applied are usually rendered three-dimensional by a finite electronic coupling between their component layers; a two-dimensional QCP has not been experimentally observed in any bulk threedimensional system, and mechanisms for dimensional reduction have remained the subject of theoretical conjecture. Here we show evidence that the Bose–Einstein condensate of spin triplets in the three-dimensional Mott insulator BaCuSi2O6 provides an experimentally verifiable example of dimensional reduction at a QCP. The interplay of correlations on a geometrically frustrated lattice causes the individual two-dimensional layers of spin-1/2 Cu2+ pairs (spin dimers) to become decoupled at the QCP, giving rise to a two-dimensional QCP characterized by linear power law scaling distinctly different from that of its three-dimensional counterpart. Thus the very notion of dimensionality can be said to acquire an ‘emergent’ nature: although the individual particles move on a three-dimensional lattice, their collective behaviour occurs in lower-dimensional space.

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79. Low temperature structural phase transition and incommensurate lattice modulation in the spin gap compound BaCuSi2O6
E. C. Samulon, Z. Islam, S. E. Sebastian, P. B. Brooks, M. K. McCourt Jr., J. Ilavsky and I. R. Fisher
Phys. Rev. B. 73, 100407(R) (2006).

ABSTRACT
Results of high resolution x-ray diffraction experiments are presented for single crystals of the spin gap compound BaCuSi2O6 in the temperature range from 16 to 300 K. The data show clear evidence of a transition from the room temperature tetragonal phase into an incommensurately modulated orthorhombic structure below ~100 K. This lattice modulation is characterized by a resolution-limited reduced wavevector q=(0,0.129+/-0.001,0) (reciprocal lattice units) referred to the orthorhombic lattice, and its 2nd and 3rd harmonics. The phase transition is first order and exhibits considerable hysteresis. This observation implies that the spin Hamiltonian representing the system is more complex than originally thought.

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78. Scanning Hall probe imaging of ErNi2B2C
H. Bluhm, S. E. Sebastian, J. W. Guikema, I. R. Fisher and K. A. Moler
Phys. Rev. B. 73, 014514 (2006).

ABSTRACT
We report scanning Hall probe imaging of ErNi2B2C in the superconducting, antiferromagnetic and weakly ferromagnetic regimes in magnetic fields up to 20 Oe, well below Hc1, with two results. First, imaging isolated vortices shows that they spontaneously rearrange on cooling through the antiferromagnetic transition temperature TN = 6 K to pin on twin boundaries, forming a striped pattern. Second, a weak, random magnetic signal appears in the ferromagnetic phase below TWFM = 2.3 K, and no spontaneous vortex lattice is present down to 1.9 K. We conclude that ferromagnetism coexists with superconductivity either by forming small ferromagnetic domains or with oscillatory variation of the magnetization on sub-penetration depth length scales.

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77. Thermodynamic and transport properties of YTe3, LaTe3 and CeTe3
N. Ru and I. R. Fisher
Phys. Rev. B. 73, 033101 (2006).

ABSTRACT
Measurements of heat capacity, susceptibility and electrical resistivity are presented for single crystals of the charge density wave compounds YTe3, LaTe3 and CeTe3. The materials are metallic to low temperatures, but have a small density of states due to the charge density wave gapping large portions of the Fermi surface. CeTe3 is found to be a weak Kondo lattice, with an antiferromagnetic groundstate and T_N = 2.8 K. The electrical resistivity of all three compounds is highly anisotropic, confirming the weak dispersion perpendicular to Te planes predicted by band structure calculations.

Link to full article.

76. Characteristic BEC scaling close to Quantum Critical Point in BaCuSi2O6
S. E. Sebastian, P. A. Sharma, M. Jaime, N. Harrison, V. Correa, L. Balicas, N. Kawashima, C. D. Batista and I. R. Fisher
Phys. Rev. B. 72, 100404(R) (2005).

ABSTRACT
We report an experimental determination of the phase boundary approaching the quantum critical point separating a quantum paramagnetic state and the proposed spin Bose-Einstein condensate of triplons in the spin dimer compound BaCuSi2O6. The ordering temperature is related to the proximity to a quantum critical point at the lower critical magnetic field Hc1 = 23.52 +/- 0.03 T by a power law parameterized by critical exponent nu. We obtain an experimental estimate of nu = 0.63 +/- 0.03 down to a temperature of 0.61 K, which is in good agreement with the mean field prediction of nu = 2/3 for the 3D Bose-Einstein condensation universality class.

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75. Evidence for charge Kondo effect in superconducting Tl-doped PbTe
I. R. Fisher, Y. Matsushita, H. Bluhm and T. H. Geballe
Proc. SPIE Vol. 5932, 59321Y (Aug. 30, 2005).

ABSTRACT
We report results of low temperature thermodynamic and transport measurements of Pb(1-x)Tl(x)Te single crystals for Tl concentrations up to the solubility limit of approximately 1.5 %. The material superconducts for x > 0.3 %, with a maximum Tc of 1.5 K for the highest Tl concentrations. All superconducting samples exhibit an anomalous resistivity upturn at low temperatures, whereas non-superconducting samples (x < 0.3%) do not. The temperature and field dependence of this resistivity upturn are consistent with a charge Kondo effect involving degenerate Tl valence states differing by two electrons, with a characteristic Kondo temperature TK ~ 6 K. The observation of such an effect supports an electronic pairing mechanism for superconductivity in this material and may account for the anomalously high Tc values.

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74. Electronic structure and charge density wave formation in LaTe1.95 and CeTe2.00
K. Y. Shin, V. Brouet, N. Ru, Z. X. Shen and I. R. Fisher
Phys. Rev. B. 72, 085132 (2005).

ABSTRACT
Results are presented of complementary measurements that probe the electronic structure and charge density wave (CDW) modulation in the quasi-2D compounds LaTe1.95 and CeTe2. Transmission electron micrographs show that the modulation wave vectors associated with the CDW are different for the two materials, and in both cases are incommensurate with the underlying lattice. These wavevectors are shown to correspond to nesting features of a simplified model of the Fermi surface. Angle Resolved PhotoEmission Spectroscopy is used to reveal the electronic structure and Fermi surface topology in the CDW state. The data indicate a large CDW gap that varies in magnitude around the Fermi surface rather differently for the two compounds. Differences in the volume of the original Fermi surface are related to the doping effect of Te vacancies. Heat capacity measurements at low temperatures indicate a very small electronic density of states, consistent with the electrical resistivity, which appears to be semiconducting or semimetallic.

Link to full article.

73. Magnetic structure of GdCo2Ge2
W. Good, J. Kim, A.I. Goldman, D. Wermeille, P. C. Canfield, Z. Islam, J. C. Lang, G. Srajer and I. R. Fisher,
Phys. Rev. B. 71, 224427 (2005).

ABSTRACT
Resonant and nonresonant magnetic x-ray scattering studies of GdCo2Ge2 were performed to determine its magnetic structure at low temperature. This compound orders in an incommensurate antiferromagnetic (AF) structure characterized by a propogation wave vector t=(0,0,tz). The value of tz is temperature dependent and approaches 0.930 reciprocal lattice units well below TN = 33.25 K. A peak corresponding to 3tz was also observed, indicating either a squaring up of the magnetic structure or the presence of a noncollinear amplitude modulated structure below TN. Fitting the angular dependence of the magnetic scattering integrated intensities to the relevant resonant and nonresonant scattering cross sections revealed that the moment direction lies primarily in the tetragonal basal plane. Scattering measurements at the Co K-edge failed to detect any resonant signal, consistent with the absence of a magnetic moment on the Co sites.

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72. High-field behavior of the spin-gap compound Sr2Cu(BO3)2
S.E. Sebastian, D. Yin, P. Tanedo, N. Harrison, G. Jorge, M. Jaime, Y. Moyzerov, G. Miller and I. R. Fisher,
Phys. Rev. B. 71, 212405 (2005).

ABSTRACT
We report magnetization and heat capacity measurements of single crystal samples of the spin gap compound Sr2Cu(BO3)2. Low-field data show that the material has a singlet ground state comprising dimers with intradimer coupling J = 100 K. High field data reveal the role of weak interdimer coupling. For fields that are large compared to the spin gap, triplet excitations are observed for significantly smaller fields than predicted for isolated dimers, indicating that weak inter-dimer coupling leads to triplet delocalization. High field magnetization behavior at low temperatures suggests additional cooperative effects.

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71. Evidence for charge Kondo effect in superconducting Tl-doped PbTe
Y. Matsushita, H. Bluhm, T. H. Geballe and I. R. Fisher,
Phys. Rev. Lett., 94, 157002 (2005).

ABSTRACT
We report results of low-temperature thermodynamic and transport measurements of Pb_{1-x}Tl_{x}Te single crystals for Tl concentrations up to the solubility limit of approximately x = 1.5%. For all doped samples, we observe a low-temperature resistivity upturn that scales in magnitude with the Tl concentration. The temperature and field dependence of this upturn are consistent with a charge Kondo effect involving degenerate Tl valence states differing by two electrons, with a characteristic Kondo temperature T_K ~ 6 K. The observation of such an effect supports an electronic pairing mechanism for superconductivity in this material and may account for the anomalously high Tc values.

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70. Fermi surface nesting and charge-density wave formation in rare-earth tritellurides
J. Laverock, S. B. Dugdale, Zs. Major, M. A. Alam, N. Ru, I. R. Fisher, G. Santi, and E. Bruno,
Phys. Rev. B. 71, 085114 (2005).

ABSTRACT
The Fermi surface of rare earth tritellurides (RTe3) is investigated in terms of the nesting-driven charge- density wave formation using positron annihilation and first-principles linear muffin-tin orbital calculations. Fermi surface nesting is revealed as a strong candidate for driving charge density wave formation in these compounds. The nesting vector obtained from positron annihilation experiments on GdTe3 is determined to be q = (0.28+/-0.02,0,0)a* (a* = 2pi/a), in excellent agreement with previous experimental and theoretical studies.

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69. Magneto-optic spectrum and electronic structure of single-crystal MnBi
D. P. Brammeier, J.-M. Park, C. G. Olsen, I. R. Fisher and D. W. Lynch,
J. Magnetism and Magnetic Materials, 283, 95-102 (2004).
ABSTRACT
Single crystals of MnBi were used for magneto-optic Kerr-angle spectroscopy and photoelectron spectroscopy. The Kerr-angle peak at 3.35 eV was observed for our nearly oxygen-free bulk samples, but the role of the oxide overlayer, demonstrated by Auger spectroscopy, as a possible origin of this peak cannot be fully assessed. The energy bands from photoelectron spectroscopy were in general agreement with calculated band structures, but were not extensive enough, due to sample cleavage properties, to distinguish reliably between band-structure calculations that disagree.

68. Fermi surface reconstruction in the CDW state of CeTe3 observed by photoemission
V. Brouet, W. L. Yang, X. J. Zhou, Z. Hussain, N. Ru, K. Y. Shin, I. R. Fisher and Z. X. Shen,
Phys. Rev. Lett, 93, 126405 (2004).

ABSTRACT
CeTe3 is a layered compound where an incommensurate charge density wave (CDW) opens a large gap (~400 meV) in optimally nested regions of the Fermi surface (FS), whereas other sections with poorer nesting remain ungapped. Through angle-resolved photoemission, we identify bands back-folded according to the CDW periodicity. They define FS pockets formed by the intersection of the original FS and its CDW replica. Such pockets illustrate very directly the role of nesting in the CDW formation but they could not be detected so far in a CDW system. We address the reasons for the weak intensity of the folded bands, by comparing different foldings coexisting in CeTe3.

Link to full article.

67. An STM and SXPS study of the interaction of C60 with the ten-fold surface of the Al72Ni11Co17 quasicrystal
E.J. Cox, J. Ledieu, V.R. Dhanak, S.D. Barrett, C.J. Jenks, I. R. Fisher, and R. McGrath,
Surface Science, 566-568, 1200-1205 (2004).

66. Structure of the ten-fold d-AlNiCo quasicrystal surface
N. Ferralis, K. Pussi, E.J. Cox, M. Gierer, J. Ledieu, I. R. Fisher, C. J. Jenks, M. Lindroos, R. McGrath, and R.D. Diehl,
Phys. Rev. B, 69, 153404 (2004).

65. Magnetic properties of single grain R-Mg-Cd primitive icosahedral quasicrystals (R = Y, Gd, Tb, Dy)
S. E. Sebastian, T. Huie, I. R. Fisher, K. W. Dennis and M. J. Kramer
Phil. Mag. B 84, 1029-1037 (2004).

ABSTRACT
The growth and characterization of single grains of the primitive icosahedral quasicrystal R-Mg-Cd (R = Y, Gd, Tb or Dy) are described. From the thermodynamic properties, it is confirmed that the system is a spin glass exhibiting the characteristic spin-freezing transition of such systems. There is no evidence for two distinct freezing transitions previously observed for polygrain samples. The bulk magnetic properties and the effect of crystalline electric fields on the spin-freezing temperature are found to be very similar to those of the face-centred icosahedral quasicrystal R-Mg-Zn.

64. Low energy electron diffraction study of Xe adsorption on the ten-fold decagonal Al-Ni-Co quasicrystal surface
N. Ferralis, R.D. Diehl, K. Pussi, M. Lindroos, I. Fisher, and C.J. Jenks,
Phys. Rev. B. 69, 075410 (2004).

63. Phonon dispersion curve of Mg-Zn-Y quasicrystals
R. A. Brand, J. Voss, F. Hippert, M. Krisch, R. Sterzel, W. Assmus and I. R. Fisher,
Journal of noncrystalline solids, 334&335, 207-209 (2004).

62. Degree of structural perfection of icosahedral quasicrystalline grainsinvestigated by synchrotron x-ray diffractometry and imaging techniques
J. Gastaldi, S. Agliozzo, A. Letoublon, J. Wang, L. Mancini, H. Klein, J. Hartwig, J. Baruchel, I. R. Fisher, T. Sato, A. P. Tsai and A. M. de Boissieu,
Phil. Mag. 83, 1-29 (2003).

61. Surface structures of approximant phases in the Al-Pd-Mn system
V. Fournee, A. R. Ross, T. A. Lograsso, J. W. Anderegg, C. Dong, K. Kramer, I.R. Fisher, P. C. Canfield, and P. A. Thiel,
Phys. Rev. B. 66, 165423 (2002).

60. Quasicrystal surfaces: potential as templates for molecular adsorption
R. McGrath, J. Ledieu, E. J. Cox, S. Haq, R. D. Diehl, C. J. Jenks, I. R. Fisher, A. R. Ross and T. A. Lograsso,
Journal of Alloys and Compounds 342, 432 (2002).

59. Transport properties of icosahedral quasicrystal Al72Pd19.5Mn8.5
A. Bilusic, Z. Budrovic, A. Smontara, J. Dolinsek, P. C. Canfield, and I. R. Fisher,
Journal of Alloys and Compounds 342, 413-415 (2002).

58. The local atomic structure of R-Mg-Zn (R=Y, Gd, Dy and Tb)
M. J. Kramer, S. T. Hong, P. C. Canfield, I. R. Fisher, J. D. Corbett, Y. Zhu, and A. I. Goldman,
Journal of Alloys and Compounds 342, 82-86 (2002).

57. The electrical conductivity of single-grain Al-Pd-Re quasicrystals
I. R. Fisher, X. P. Xie, I. Tudosa, C. W. Gao, C. Song, P. C. Canfield, A. Kracher, K. Dennis, D. Abanoz and M.J. Kramer
Phil. Mag. B 82, 1089 (2002).

ABSTRACT
Systematic electrical transport data are presented for single quasicrystals in the Al-Pd-Re family across the accessible width of formation. The temperature dependence of the electrical conductivity can be accounted for in terms of weak localization and electron-electron interactions for all compositions studied, in contrast to previous studies of cast and annealed polygrain material. These results indicate that the conductivity mechanism in the Al-Pd-Re system is not dramatically different from that of other quasicrystal families.

56. Surface preparation and characterization of the icosahedral Al-Ga-Pd-Mn quasicrystal
M. Heinzig, C. J. Jenks, M. Van Hove, I. R. Fisher, P. C. Canfield and P. A. Thiel,
J. Alloys and Compounds 338, 248-252 (2002).

55. The ten-fold surface of the decagonal Al72Ni11Co17 quasicrystal studied by LEED, SPA-LEED, AES and STM
E. J. Cox, J. Ledieu, R. McGrath, R. D. Diehl, C. J. Jenks, and I. R. Fisher,
Materials Research Society Symposium Proceedings (2001), 643, K11.3.1-K11.3.6 (2002).

54. The thermal stability of a single-grain Mg-Zn-Y icosahedral quasicrystal
Z. P. Luo, Y. L. Tang, D. J. Miller, M. J. Kramer, I. R. Fisher, and P. C. Canfield,
Materials Research Society Symposium Proceedings (2001), 643, K9.4.1-K9.4.6 (2002).

53. The influence of growth rate on porosity in icosahedral Al-Pd-Mn quasicrystals,
A. R. Ross, I. R. Fisher, P. C. Canfield and T. A. Lograsso,
Materials Research Society Symposium Proceedings (2001), 643, K1.5.1-K1.5.5. (2002).

52. Icosahedral quasicrystal Al-Pd-Mn and its xsi' approximant: linear expansivity, specific heat, magnetic susceptibility, electrical resistivity and elastic constants
C. Swenson, I. R. Fisher, N. E. Anderson Jr., P. C. Canfield and A. Migliori,
Phys. Rev. B. 65, 184206 (2002).

51. Microwave conductivity and penetration depth in the heavy fermion superconductor CeCoIn5
R. J. Ormeno, A. Sibley, C. E. Gough, S. Sebastian and I. R. Fisher,
Phys. Rev. Lett. 88, 047005 (2002).

50. Infrared and optical properties of pure and cobalt doped LuNi2B2C
M. Windt, J. J. McGuire, T. Room, A. Pronin, T. Timusk, I. R. Fisher, and P. C. Canfield,
Phys. Rev. B. 65, 064506/1-064506/9 (2002).

49. High-temperature solution growth of single crystals and quasicrystals
P. C. Canfield and I. R. Fisher,
J. Crystal Growth, 225, 155-161 (2001).

48. Observation of a spin reorientation in TbCu2Ge2 from resonant and non-resonant x-ray scattering
C. Song, D. Johnson, D. Wermeille, A. I. Goldman, S. L. Bud'ko, I. R. Fisher, and P. C. Canfield,
Phys. Rev. B 64, 224414 (2001).

47. Unusual spin glass phase in icosahedral Tb-Mg-Zn quasicrystals
J. Dolinsek, Z. Jaglicic, M. A. Chernikov, I. R. Fisher, and P. C. Canfield,
Phys. Rev. B 64, 224209 (2001).

46. Reentrant behavior in the temperature dependence of metamagnetic transitions in single crystal Nd6Fe13-xAl1+x
R. W. McCallum, I. R. Fisher, N. E. Anderson, P. C. Canfield, M. J. Kramer and K. W. Dennis
IEEE Transactions on Magnetics 37(4, Pt. 1), 2147 (2001).

45. R9Mg34Zn57 icosahedral quasicrystals: The tuning of a model spin glass
P.C. Canfield and I.R. Fisher,
J. Alloys and Compounds 317-318, 443-447 (2001).

44. Structure and physical properties of the new Pseudo-binary intermetallic compound Ti11(Sb,Sn)8
H. Kim, M.M. Olmstead, J.Y. Chan, P.C. Canfield, I.R. Fisher, R.W. Henning, A.J. Schultz and S.M. Kauzlarich,
J. Solid State Chemistry 157, 225-232 (2001).

43. Investigation of the effect of Ga doping on the thermoelectric properties of the A1PdMn quasicrystalline system.
D.W. Winkler, A.L. Pope, T.M. Tritt, I.R. Fisher, T.A. Wiener and P.C. Canfield,
Proc. 18th Int. Conf. Thermoelectr. 398-401 (1999).

42. Plasticity of icosahedral Zn-Mg-Dy single quasicrystals
M. Heggen, P. Schall, M. Feuerbacher, H. Klein, I. R. Fisher, P.C. Canfield and K. Urban,
Materials Science and Engineering A 294-296, 781-785 (2000).

41. Heat capacities of icosahedral and hexagonal phases of Zn-Mg-Y system
A. Inaba, H. Takakura, A. P. Tsai, I. R. Fisher, and P. C. Canfield,
Materials Science & Engineering, A 294-296 723-726 (2000).

40. Electrical resistivity, thermopower, and thermal conductivity of single-grained (Y, Tb, Ho, Er)-Mg-Zn icosahedral quasicrystals.
K. Gianno, A.V. Sologubenko, M.A. Chernikov, H.R. Ott, I. R. Fisher and P.C. Canfield,
Materials Science and Engineering A 294-296, 715-718 (2000).

39. Diffusion of 57Co in decagonal Al-Ni-Co quasicrystals
C. Khoukaz, R. Galler, H. Mehrer, P.C. Canfield, I.R. Fisher and M. Feuerbacher
Materials Science and Engineering A 294-296, 697-701 (2000).

38. Phason strain and structural perfection in the R-Mg-Zn icosahedral phases
A. Letoublon, I.R. Fisher, T.J. Sato, M. de Boissieu, M. Boudard, S. Agliozzo, L. Mancini, J. Gastaldi, P.C. Canfield, A.I Goldman and A.P. Tsai,
Materials Science and Engineering A 294-296, 127-130 (2000).

37. Formation and morphological development of porosity in icosahedral Al-Pd-Mn alloys.
A. R. Ross, T.A. Wiener, I.R. Fisher, P.C. Canfield and T.A. Lograsso,
Materials Science and Engineering A 294-296, 53-56 (2000).

36. Growth of large single-grain quasicrystals from high-temperature metallic solutions
I.R. Fisher, M.J. Kramer, Z. Islam, T.A. Wiener, A. Kracher, A.R. Ross, T.A. Lograsso, A.I. Goldman and P.C. Canfield,
Materials Science and Engineering A 294-296, 10-16 (2000).

35. Design of a metallic Ising spin glass in the Y1-xTbxNi2Ge2 system
T.A. Wiener, I. R. Fisher, S.L. Bud'ko, A. Kracher and P.C. Canfield,
Phys. Rev. B. 62, 15056-15066 (2000).

34. Nonlocal effects in magnetization of high-kappa superconductors
V.G. Kogan, S.L. Bud'ko, I. R. Fisher and P.C. Canfield,
Phys. Rev. B. 62, 9077-9082 (2000).

33. Observation of a metamagnetic phase transition in an itinerant 4f system via the magneto-optic Kerr effect: Ce(Fe1-xCox)2
R.J. Lange, I.R. Fisher, P.C. Canfield, V.P. Antropov, S.J. Lee, B.N. Harmon and D.W. Lynch,
Phys. Rev. B. 62, 7084-7092 (2000).

32. Yb14ZnSb11: charge balance in Zintl compounds as a route to intermediate Yb valence
I.R. Fisher, S.L. Bud'ko, C. Song, P.C. Canfield, T.C. Ozawa and S.M. Kauzlarich,
Phys. Rev. Lett. 85, 1120-1123 (2000).

31. Low-temperature thermal conductivity of a single-grain Y-Mg-Zn icosahedral quasicrystal
K. Giannò, A.V. Sologubenko, M.A. Chernikov, H.R. Ott, I.R. Fisher, and P.C. Canfield,
Phys. Rev. B 62, 292-300 (2000).

30. Low-temperature transport, thermal and optical properties of single-grain quasicrystals of icosahedral phases in the Y-Mg-Zn and Tb-Mg-Zn alloy systems
M.A. Chernikov, S. Paschen, E. Felder, P. Vorburger, B. Ruzicka, L. Degiorgi, H.R. Ott, I.R. Fisher, and P.C. Canfield,
Phys. Rev. B 62, 262-272 (2000).

29. Non-locality and the flux line lattice square to hexagonal symmetry transition in the borocarbide superconductors
M.R. Eskildsen, I.R. Fisher, P.L. Gammel, D.J. Bishop, N.H. Andersen, K. Mortensen and P.C. Canfield,
Physica C 332, 320-326 (2000).

28. The magnetic characteristics of the Tb(Ni1-xCox)2Ge2 system
T.A. Wiener, I.R. Fisher and P.C. Canfield,
J. Alloys and Compounds 303-304, 289-292 (2000).

27. Magnetic properties of icosahedral R-Mg-Zn quasicrystals
I.R. Fisher, Z. Islam J. Zarestky, C. Stassis, M.J. Kramer, A.I. Goldman and P.C. Canfield,
J. Alloys and Compounds 303-304, 223-227 (2000).

26. Recent advances in the study of quasicrystals
I.R. Fisher, M.J. Kramer and A.I. Goldman,
Micron 31, 469-473 (2000).

25. Interwoven magnetic and flux line structures in single crystal (Tm,Er)Ni2B2C
P.L. Gammel, D. Lopez, D.J. Bishop, M.R. Eskildsen, N.H. Andersen, K. Mortensen, I.R. Fisher, K.O. Cheon and P.C. Canfield
Journal of Applied Physics 87, 5544-5548 (2000).

24. A comparison of structural stabilities of the three high-symmetry surfaces of Al-Pd-Mn bulk quasicrystals using LEED
Z. Shen, W. Raberg, M. Heinzig, C.J. Jenks, V. Fournée, M.A. Van Hove, T.A. Lograsso, D. Delaney, T. Cai, P.C. Canfield, I.R. Fisher, A.I. Goldman, M.J. Kramer, and P.A. Thiel
Surface Science 450, 1-11 (2000).

23. Optical properties and electronic structure of single crystals of LuAl2 and YbAl2
S.J. Lee, S.Y. Hong, I.R. Fisher, P.C. Canfield, B.N. Harmon and D.W. Lynch
Phys. Rev. B 61, 10076-10083 (2000).

22. Plastic deformation of icosahedral Zn-Mg-Dy single quasicrystals
M. Heggen, M. Feuerbacher, P. Schall, H. Klein, I.R. Fisher, P.C. Canfield and K. Urban
Phil. Mag. Letters, 80, 129-136 (2000).

21. Nesting properties and anisotropy of the Fermi surface of LuNi2B2C
S.B. Dugdale, M.A. Alam, I. Wilkinson, R.J. Hughes, I.R. Fisher, P.C. Canfield, T. Jarlborg and G. Santi,
Phys. Rev. Lett. 83, 4824-4827 (1999).

20. On the growth of icosahedral Al-Pd-Mn quasicrystals from the ternary melt
I.R. Fisher, M.J. Kramer, T.A. Wiener, Z. Islam, A.R. Ross, T.A. Lograsso, A. Kracher, A.I. Goldman and P.C. Canfield,
Phil. Mag. B 79, 1673-1684 (1999).

19. Critical doping in overdoped high-Tc superconductors: a quantum critical point?
J.L. Tallon, J.W. Loram, G.V.M. Williams, J.R. Cooper, I.R. Fisher, J.D. Johnson, M.P. Staines and C. Bernhard,
Physica Status Solidi B 215, 531-540 (1999).

18. Anisotropy and metamagnetism in the RNi2Ge2 (R = Y, La-Nd, Sm-Lu) series
S.L. Bud'ko, Z. Islam, T.A. Wiener, I.R. Fisher, P.C. Canfield and A.H. Lacerda
J. Magn. Magn. Mat. 205, 53 - 78 (1999).

17. Systematic study of anisotropic transport and magnetic properties of RAgSb2 (R = Y, La-Nd, Sm, Gd-Tm)
K.D Myers, S.L. Bud'ko, I.R. Fisher, Z. Islam, H. Kleinke, P.C. Canfield and A.H. Lacerda,
J. Magn. Magn. Mat. 205, 27 - 52 (1999).

16. Magnetic and transport properties of single-crystal R2Cu2In (R = Gd-Tm, Lu)
I.R. Fisher, Z. Islam and P.C. Canfield,
J. Magn. Magn. Mat. 202, 1-10 (1999).

15. Thermodynamic and Transport Properties of Single-Crystal Yb14MnSb11
I.R. Fisher, T. A. Wiener, S. L. Bud'ko P. C. Canfield, J. Y. Chan and S. M. Kauzlarich,
Phys. Rev. B 59, 13829-13834 (1999).

14. Systematic studies of the square-hexagonal flux line lattice transition in Lu(Ni1-xCox)2B2C: the role of non-locality
P.L. Gammel, D.J. Bishop, M.R. Eskildsen, K. Mortensen, N.H. Andersen, I.R. Fisher, K.O. Cheon, P.C. Canfield and V.G. Kogan,
Phys. Rev. Lett. 82, 4082-4085 (1999).

13. On the growth of decagonal Al-Ni-Co quasicrystals from the ternary melt
I.R. Fisher, M.J. Kramer, Z. Islam, A.R. Ross, A. Kracher, T. Wiener, M.J. Sailer, A.I. Goldman and P.C. Canfield,
Phil. Mag. B 79, 425-434 (1999).

12. Boron isotope effect in single-crystal YNi2B2C and LuNi2B2C superconductors
K.O. Cheon, I.R. Fisher and P.C. Canfield,
Physica C 312, 35-39 (1999).

11. Magnetic and transport properties of single-grain R-Mg-Zn icosahedral quasicrystals [R = Y, (Y1-xGdx), (Y1-xTbx), Tb, Dy, Ho and Er]
I.R. Fisher, K.O. Cheon, A.F. Panchula, P.C. Canfield, M. Chernikov, H.R. Ott, and K. Dennis,
Phys. Rev. B 59, 308-321 (1999).

10. Resistivity and magnetic susceptibility of single-crystal Lu(Ni1-xCox)2B2C
K.O. Cheon, I.R. Fisher, V.G. Kogan, P.C. Canfield, P. Miranovic and P.L. Gammel,
Phys. Rev. B 58, 6463-6467 (1998).

9. Reinvestigation of long-range magnetic ordering in icosahedral Tb-Mg-Zn
Z. Islam, I.R. Fisher, J. Zarestky, P.C. Canfield, C. Stassis and A.I. Goldman
Phys. Rev. B 57, R11047-R11050 (1998).

8. Growth of large-grain R-Mg-Zn quasicrystals from the ternary melt (R = Y, Er, Ho, Dy and Tb)
I.R. Fisher, Z. Islam, A.F. Panchula, K.O. Cheon, M.J. Kramer, P.C. Canfield and A.I. Goldman,
Phil. Mag. B 77, 1601-1615 (1998).

7. Anisotropic resistivity and normal-state magnetoresistance of RNi2B2C (R = Y, Lu, Er, Ho)
I.R. Fisher, J.R. Cooper and P.C. Canfield,
Phys. Rev. B 56, 10820-10823 (1997).

6. Angular dependence of the c-axis normal-state magnetoresistance in single-crystal Tl2Ba2CuO6
N.E. Hussey, J.R. Cooper, J.M. Wheatley, I.R. Fisher, A. Carrington, A.P. Mackenzie, C.T. Lin and O. Milat,
Phys. Rev. Lett. 76, 122-125 (1996).

5. Angular dependence of the c-axis normal-state magnetoresistance in single-crystal Tl2Ba2CuO6
N.E. Hussey, J.R. Cooper, I.R. Fisher, A.P. Mackenzie and J.M. Wheatley,
Proc. 10th Anniv HTS Workshop Phys., Mater. Appl., (Ed. B. Batlogg, World Scientific, Singapore) p330-331 (1996).

4. Normal-state properties of RNi2B2C (R = Y, Ho, La) and anisotropic resistivity of single-crystal RNi2B2C (R = Lu, Er, Ho)
I.R. Fisher, J.R. Cooper, K.R. Locherer, R.J. Cava and P.C. Canfield
J. Low T. Phys. 105, Nos. 5/6, 1623-1628 (1996).

3. Effect of sample density on the resistivity and Hall coefficient of polycrystalline La1.83Sr0.17CuO4
I.R. Fisher and J.R. Cooper,
Physica C 272, 125-130 (1996).

2. Normal-state transport and magnetic properties of RNi2B2C (R = Y, Ho, La)
I.R. Fisher, J.R. Cooper and R.J. Cava,
Phys. Rev. B 52, 15086-15089 (1995).

1. Hall effect and thermoelectric power of Y0.9Ca0.1Ba2Cu3O7-delta
I.R. Fisher, P.S.I.P.N. de Silva, J.W. Loram, J.L. Tallon, A. Carrington and J.R. Cooper,
Physica C 235-240, 1497-1498 (1994).

Fisher Research Group
Geballe Laboratory for Advanced Materials
Dept. of Applied Physics
Stanford University
CA 94305-4045
 Last updated Sept. 21st 2009