Events - Daily
November 25, 2013 >>
|Monday, November 25|
Condensed Matter Seminar, Victor Galitski, "Topological Kondo Insulator"
In this talk I will review recent theoretical work on a new class of topological material systems - topological Kondo insulators, which appear as a result of interplay between strong correlations and spin-orbit interactions. I will start with introducing the by now standard theory of topological band insulators and explain the Fu-Kane method to calculate the Z2 topological index for time-reversal-invariant band structures in three dimensions. The method will be used to show that hybridization between the conduction electrons and localized f-electrons in certain heavy fermion compounds gives rise to interaction-induced topological insulating behavior. A mean field theory of these Kondo topological insulators will be derived. I will also discuss recent experimental results, which have conclusively confirmed our predictions in the Samarium hexaboride compound, where the long-standing puzzle of the residual low-temperature conductivity has been shown to originate from topological surface states. This material system represents the first true topological insulator observed experimentally with low-temperature transport dominated by the surface and essentially no conduction in the bulk. In conclusion, I will mention our ongoing theory work, which focuses on very unusual non-linear transport properties of Samarium hexaboride devices, which mimic neuron-like behavior in biological systems.
PCTS Seminar Room · 1:15 p.m.– 2:30 p.m.
High Energy Theory Seminar - Eva Silverstein, Stanford - "New solutions with accelerated expansion in string theory and applications"
We present concrete solutions with accelerated expansion in string theory, requiring a small, tractable list of stress energy sources. We explain how this construction (and others in progress) evades previous no go theorems for simple accelerating solutions. Our solutions respect an approximate scaling symmetry and realize discrete sequences of values for the equation of state, including one with an accumulation point at w=-1 and another accumulating near w=-1/3 from below. In another class of models, a density of defects generates scaling solutions with accelerated expansion. We briefly discuss potential applications to dark energy phenomenology, and to holography for cosmology.
PCTS Seminar Room · 2:30 p.m.– 3:30 p.m.