Anomalous acceleration and the role of quantum geometry in semimetals and flat bands

  Tobias Holder  ,  Daniel Kaplan  ,  Binghai Yan  
Weizmann Institute of Science

While transport properties are often determined by the semiclassical velocity of the quasiparticle, here I will talk about gapped and semimetallic materials which depart from this canonical picture and where it is necessary to account for additional components of the electronic motion which are most easily envisaged as quasiparticle accelerations. This is particularly pronounced in the bulk photovoltaic effect, a second-order optical response in which incident light is converted into a dc-current. This current can be viewed as the result of acceleration terms which give access to many details of the band structure geometry. As examples I discuss the role of Berry charges in Weyl semimetals and a large current response in the terahertz regime in twisted bilayer graphene.