CMP Kid's journal club at Stanford

Inna Vishik, Shen group
Title:
Laser ARPES studies on Bi-2212s
abstract:
Angle-resolved photoemission spectroscopy (ARPES) utilizes the photoelectric effect to study how electrons move in a crystalline material, like a microscope in momentum-space. Laser-based ARPES is a new technique which allows rapid aquisition of high-resolution ARPES data with superior statistics. The improved resolution of laser ARPES allows reliable access to fine structures in the spectrum, and has recently been used to observe a new kink at low energy (<10meV) in Bi-2212. I will discuss the doping-dependent systematics of this low-energy kink. We find that the kink gets stronger with decreasing doping, which leads to a doping-dependent nodal Fermi velocity. This is in contrast to earlier experiments, done with poorer resolution, which suggested that the nodal Fermi velocity is independent of doping. I will also discuss the implications these results have on our understanding of bulk transport measurements.

Beth Nowadnick, Devereaux group
Title:
Polarons in the Colossal Magnetoresistive Manganites
abstract:
Colossal magnetoresistance (CMR), the ability of a material to change its resistance by several orders of magnitude in a magnetic field, was first observed in the manganites in 1993. Although CMR offers great potential for technological application, for example in data storage, the physics of the effect has not yet been understood. I will review a few papers about recent work on the physics of the CMR manganites, including ARPES studies of polarons in the manganites, as well as work on nanoscale phase separation in these materials.

Srinivas Raghu
Title:
Coexistence of Ferromagnetism and superconductivity in heavy electron superconductors
abstract:
I will discuss several uranium based systems that exhibit both ferromagnetism and superconductivity
simultaneously under the application of pressure. I will review the experimental status of three such
materials: UGe2, UCoGe, and URhGe, and will discuss why I find them to be interesting.

Suk-Bum Chung, SITP
Title:
Detecting the Majorana fermion surface state of $^3$He-B through spin relaxation

abstract:
The concept of the Majorana fermion has been postulated more than eighty years ago; however, this elusive particle has never been observed in nature. The non-local character of the Majorana fermion can be useful for topological quantum computation. Recently, it has been shown that the 3He-B phase is a time-reversal invariant topological superfluid, with a single component of gapless Majorana fermion state localized on the surface. Such a Majorana surface state contains half the degrees of freedom of the single Dirac surface state recently observed in topological insulators. We show here that the Majorana surface state can be detected through an electron spin relaxation experiment. The Majorana nature of the surface state can be revealed though the striking angular dependence of the relaxation time on the magnetic field direction, $1/T_1 \propto sin^2 \theta$ where $\theta$ is the angle between the magnetic field and the surface normal. The temperature dependence of the spin relaxation rate can reveal the gapless linear dispersion of the Majorana surface state. We propose a spin relaxation experiment setup where we inject an electron inside a nano-sized bubble below the helium liquid surface.

Jiun-Haw, Fisher group
Title:
The Phase Digram and Domain Wall Motion in the Iron Pnictides Materials

abstract:
The cobalt doped BaFe2As2 is one of the well characterized families of iron pnictides superconductors. The single magnetic/structural transition of the parent compound splits into two transitions by cobalt doping. Both transitions are suppressed with increasing doping concentration and eventually the superconductivity emerges. On the other hand, twinning domains appear in the underdoped compounds due to the tetragonal to orthorhombic structural transition. In this talk I will show you how we determine the phase digram of this materials by means of thermodynamic, transport and scattering measurements. I will also talk about how we might affect the domain structures in the underdoped compounds.

Lisa Qian, Moler group
Title:
Magnetic Cellular Quantum Automata

abstract:
Moore's Law has more or less held for the past 40 years and has been the standard for the semiconductor industry. But we are now approaching fundamental limits in CMOS technology that prevents this scaling from continuing. One candidate to replace MOSFETs is magnetic cellular quantum automata (MCQA). In this technology, coupled nanomagnets are used for logic gates and to propagate information. I will a review of a few papers that give an idea of the progress in this field.

Françoise Kidwingira, KGB group
Title:
Scanning Tunneling Potentiometry

abstract:
Scanning Tunneling Potentiometry is an STM based technique that measures the local electrochemical potential. I will describe the operating principles, main challenges, and applications in the last 25 years as it struggled to become a mainstream technique.

Sho Yaida, Shenker group
Title:
Impressionistic Introduction to Holographic Dictionaries

abstract:
In the first 1/3 of the talk, we will see how useful (or useless) string theory can be for the study of condensed matter systems in strongly coupled regime, providing us powerful tools known as ``Holographic Dictionaries."
In the second 1/3, we will review applications of holographic dictionaries to the study of phenomena such as quantum criticality, superfluidity/superconductivity, non-Fermi liquid behavior, etc.
For the last 1/3, I will advertise my recent work with S. Kachru and A. Karch (0909.2639) on the construction of novel systems, including a holographic model of ``glass."
I will keep the use of equations to the bare minimum and focus on conceptual aspects with many pictures, so that hopefully everyone can get something out of it (on top of pizza).

Lan Luan, Moler group
Title:
Measuring the local penetration depth with scanning probes

abstract:
I want to review a few of the conventional methods people use to measure the penetration depth in superconductors. Then I'd like to talk about our ongoing research on using Magnetic Force Microscope (MFM) and SQUID to measure the penetration depth, both its absolute value and the change with temperature.