Z2 peak of noise correlations in a quantum spin Hall insulator

We investigate the current noise correlations at a quantum point contact in a quantum spin Hall structure, focusing on the effect of a weak magnetic field in the presence of disorder. For the case of two equally biased terminals we discover a robust peak: the noise correlations vanish at $B = 0$ and are negative for $B\not = 0$. We find that the character of this peak is intimately related to the interplay between time reversal symmetry and the helical nature of the edge states and call it the Z2 peak.Comment: 4+epsilon pages, 3 figure

Quantum critical origin of the superconducting dome in SrTiO3_3

We investigate the origin of superconductivity in doped SrTiO$_3$ (STO) using a combination of density functional and strong coupling theories within the framework of quantum criticality. Our density functional calculations of the ferroelectric soft mode frequency as a function of doping reveal a crossover from quantum paraelectric to ferroelectric behavior at a doping level coincident with the experimentally observed top of the superconducting dome. Based on this finding, we explore a model in which the superconductivity in STO is enabled by its proximity to the ferroelectric quantum critical point and the soft mode fluctuations provide the pairing interaction on introduction of carriers. Within our model, the low doping limit of the superconducting dome is explained by the emergence of the Fermi surface, and the high doping limit by departure from the quantum critical regime. We predict that the highest critical temperature will increase and shift to lower carrier doping with increasing $^{18}$O isotope substitution, a scenario that is experimentally verifiable.Comment: 4 pages + supplemental, 3 + 2 figure

Probing ultracold Fermi gases with light-induced gauge potentials

We theoretically investigate the response of a two component Fermi gas to vector potentials which couple separately to the two spin components. Such vector potentials may be implemented in ultracold atomic gases using optically dressed states. Our study indicates that light-induced gauge potentials may be used to probe the properies of the interacting ultracold Fermi gas, providing. amongst other things, ways to measure the superfluid density and the strength of pairing.Comment: 8 pages, 3 figure