“Berry phases and the intrinsic thermal Hall effect in high temperature cuprate superconductors” by Oskar Vafek (Florida State University)

Date: 
Wednesday, September 17, 2014 - 4:00pm to 5:00pm
Series: 
Condensed Matter Physics Seminar

Condensed Matter Physics Seminar

Physics and Astronomy Building (PAB) Room 4-330
Wednesday, September 17, 2014
4-5pm

Guest Speaker: Oskar Vafek (Florida State University)

Talk Title: Berry phases and the intrinsic thermal Hall effect in high temperature cuprate superconductors

Abstract:

The low energy excitations of a superconductor, the so called Bogoliubov quasiparticles, are a quantum mechanically coherent superposition of an electron and a hole. As such, they do not carry a fixed electrical charge. In the vortex state of an extreme type-II superconductor, such as high Tc cuprates, the externally applied magnetic field H penetrates the sample in the form of flux tubes, whose width, set by the penetration depth, is much larger than the intervortex separation (set by the magnetic length), for essentially the entire range of H-field applied in a typical experiment. Therefore, the quasiparticles move in a practically uniform magnetic (induction) field B.

Do the quasiparticles experience a Lorentz force when set in motion by an externally applied heat current, bending their trajectories and causing the temperature gradient perpendicular to the heat current and the applied field H, or is the thermal Hall effect a consequence of Berry phases as in an intrinsic anomalous Hall effect of a semiconductor/metal with spin-orbit coupling? In this talk I will show that it is the latter. I will also present a calculation of the full temperature, H-field and the d-wave pairing gap dependence of the intrinsic thermal Hall conductivity.

We find that the intrinsic contribution to the thermal Hall conductivity displays a rapid onset with increasing temperature, which compares favorably with existing experiments at high H-fields on the highest purity samples. This finding may help to settle a much-debated question of the bulk value of the pairing strength in cuprate superconductors in magnetic field.

V. Cvetkovic and O. Vafek, arXiv:1407.6002.