Title: New Hall effect goes nonlinear 

Time: 14:00-15:00, Thursday, 2021/09/09

The link for the online seminar : 
Google Meet joining info
https://meet.google.com/htj-dwhd-zpz

Abstract:
 In this talk I will introduce our recent study of the nonlinear Hall effect in materials with time-reversal symmetry. In the absence of a magnetic field, the Hall effect in the linear response regime vanishes due to time-reversal symmetry. However, a transverse charge current can still occur in second-order response to an external electric field, as a result of the Berry curvature dipole (BCD) in momentum space. Candidate 2D materials to observe this effect are two-dimensional transition-metal dichalcogenides (TMDCs).
The application of strain and electrical displacement field can systematically control the BCD in TMDCs. We also demonstrate that 3D giant-Rashba material bismuth tellurium iodine (BiTeI) exhibits a pressure-driven phase transition between topological and trivial insulators, which is accompanied by a giant enhancement of the BCD which can be probed in transport and optoelectronic experiments.
While there has been much effort to understand nonlinear transport due to a BCD in bulk, we further find that the topological materials with a conducting surface, like Weyl Fermi arcs, could host a surface BCD. 
Weyl Fermi arcs are generically accompanied by a divergence of the surface Berry curvature scaling as 1/k^2, where k is the distance to a hot-line in the surface Brillouin zone that connects the projection of Weyl nodes with opposite chirality but which is distinct from the Fermi arc itself.
This divergence is reflected in a variety of Berry curvature mediated effects that are readily accessible experimentally, and in particular leads to a surface Berry curvature dipole that grows linearly with the thickness of a slab of a Weyl semimetal material in the clean limit. This implies the emergence of a gigantic contribution to the non-linear Hall effect in such devices. 

Ref: 
1. J.-S. You, S. Fang, S.-Y. Xu, E. Kaxiras and T. Low, Phys. Rev. B 98, 121109 (2018). 
2. J. I. Facio, D. Efremov, K. Koepernik, J.-S. You, I. Sodemann, and J. van den Brink, Phys. Rev. Lett. 121, 246403 (2018). 
3. X.-Q. Yu, Z.-G. Zhu, J.-S. You, T. Low, G. Su, Phys. Rev. B 99, 201410 (2019). 
4. D. Wawrzik, J.-S. You, J. I. Facio, J. van den Brink, I. Sodemann, Phys. Rev. Lett. 127, 056601 (2021) (Editors' Suggestion).