Abstract: In solid materials, electrons are usually described by the non-relativistic Schrodinger equationsince electron velocity is much slower than the speed of light. However, the relativisticDirac/Weyl equation can emerge as a low-energy effective theory for electrons in certainmaterials. These systems are dubbed “Dirac/Weyl materials” and provide a tunable platformto test quantum relativistic phenomena in table-top experiments. Owing to the linear-inmomentum form, a variety of physical fields, e.g. strain and phonons, can couple toDirac/Weyl quasi-particles in a similar form as the minimal gauge coupling. These physicalfields thus are dubbed the “pseudo-gauge field”, which provides a useful theoretical conceptto understand or predict a variety of physical phenomena beyond the electromagneticresponse in Dirac/Weyl materials. In this talk, I will focus on the physical phenomena relatedto the pseudo-gauge field created by strain and phonons. I will first discuss the Berrycurvature contribution to the piezo-electric response, which can be understood as the Hallcurrent response driven by strain-induced pseudo-electric field [1]. Our theory predicts ajump of piezo-electric coefficients across a topological phase transition in 2D Diracmaterials. Then I will show that electron-phonon interaction in 2D Dirac materials also takesa gauge coupling form, and consequently, electron Berry curvature can appear in the effectiveaction of phonon dynamics [2]. This leads to a “helical texture” of phonon angularmomentum in the momentum space, from which a heat current can drive a total phononangular momentum. Finally, I will show phonons can also induce a gravitational torsion fieldfor the Kramers-Weyl fermions in chiral crystals and discuss the possibility of probing theNieh-Yan anomaly through thermal transport measurement [3].
References:
[1] Piezoelectricity and topological quantum phase transitions in two-dimensional spin-orbitcoupled crystals with time-reversal symmetry, Jiabin Yu, Chao-Xing Liu, NatureCommunications 11, 2290 (2020).
[2] Phonon Helicity Induced by Electronic Berry Curvature in Dirac Materials, Lun-Hui Hu,Jiabin Yu, Ion Garate, Chao-Xing Liu, Phys. Rev. Lett. 127, 125901, 2021
[3] Probing Nieh-Yan Anomaly through phonon dynamics in the Kramers-Weyl semimetalsof Chiral Crystals, Chao-Xing Liu, arXiv:2104.04859, 2021.
Location: ATL 4402