How to detect Berry phase in graphene without magnetic field?

摘要

We discuss the topological properties of graphene superlattices excited by ultrafast circularly-polarized laser pulses with strong electric field amplitude, aiming to directly observe of the Berry phase, a geometric quantum phase encoded in the graphene's electronic wave function. As a continuing research on our recent paper, Phys. Rev. B 96, 075409, we aim to show that the broken symmetry system of graphene superlattice and the Bragg reflection of electrons creates diffraction and "which way" interference in the reciprocal space reducing the geometrical phase shift and making it directly observable in the electron interferograms. Such a topological phase shift acquired by a carrier moving along a closed path of crystallographic wave vector is predictably observable via time and angle resolved photoemission spectroscopy (tr-ARPES). We believe that our result is an essential step in control and observation of ultrafast electron dynamics in topological solids and may open up a route to all-optical switching, ultrafast memories, and petahertz-scale information processing technologies.