290S/290K Quantum Materials Seminar speaker Tobias Holder (Weizmann Institute) on Wednesday, April 26 at 2 pm in Physics South 402

Time/Venue Wednesday, April 26 at 2 pm in Physics South 402 and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09
Host Johannes Mitscherling / Joel Moore
Title Vortices and para-hydrodynamics in ultraclean WTe2 flakes
Abstract Electron hydrodynamics, which is the viscous flow of current in mesoscopic high-mobility devices, has become a valuable tool in characterizing quantum materials, and can be used to (re)create a number of hydrodynamic phenomena. However, the formation of a whirlpool – arguably the most striking hydrodynamic phenomenon – has so far been elusive.
I discuss recent results on ultrapure, thin WTe2 flakes in which it is for the first time possible to directly observe hydrodynamic vortices using spatially resolved current-imaging techniques. From a theory perspective, this observation is rather challenging: Both from the measured bulk mean free path and from ab-initio calculations, one would instead expect ballistic transport, and not hydrodynamic flow. Here, I show how this discrepancy can be resolved in a kinetic theory that incorporates weak surface scattering from the top and bottom surfaces, thereby leading to a novel para-hydrodynamic regime where ballistic and hydrodynamic mechanisms coexist. Surprisingly, our findings imply that para-hydrodynamic transport appears generically in ultraclean devices, meaning it might be observable in a range of other currently studied materials. [2202.02798,2207.13894]