Research: Spin gap compounds

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		An interesting class of magnetic materials is those for which the spectrum of magnetic excitations is characterized by a separation of the first excited state from the ground state by a significant amount of energy, the spin gap. Compounds that are composed of weakly interacting magnetic dimers fall in to this class of material. The spin gap can be closed by applying a large magnetic field, and several exotic magnetic states have been proposed for such compounds in this regime, including a BEC of delocalized triplets. We are currently investigating two different families of complex copper oxides that are based on weakly coupled magnetic dimers, with the aims of better understanding the magnetic excitations and high-field states of such materials. The figure shows the low-field susceptibility of one of these materials, Sr2Cu(BO3)2. The red line is a fit to a model of isolated dimers, from which the intradimer exchange constant can be estimated. High field measurements are used to reveal the effects of weak interdimer coupling. The inset shows a piece chipped from a larger single crystal, grown via TSFZ.
Recent publications
High field behavior of the spin gap compound Sr2Cu(BO3)2 Characteristic BEC scaling close to QCP in BaCuSi2O6 Low temperature structural phase transition and incommensurate lattice modulation in the spin gap compound BaCuSi2O6 Dimensional reduction at a quantum critical point Role of anisotropy in the spin dimer compound BaCuSi2O6 Bose-Einstein condensation in BaCuSi2O6 Multiple Magnon Modes and Consequences for the Bose-Einstein Condensed Phase in BaCuSi2O6 Geometric Frustration and Dimensional Reduction at a Quantum Critical Point Nuclear magnetic resonance evidence for a strong modulation of the Bose-Einstein condensate in BaCuSi2O6 Ordered magnetic phases of the frustrated spin-dimer compound Ba3Mn2O8
Contacts
Suchitra Sebastian Eric Samulon Ian Fisher
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