Unifying Optical Selection Rules for Excitons in Two Dimensions: Band Topology and Winding Numbers

ORAL

Abstract

We show that band topology can dramatically change the photophysics of two-dimensional semiconductors. For systems in which states near the band extrema are of multi-component character, the spinors describing these components (pseudospins) can pick up nonzero winding numbers around the extremal k-point. In these systems, we find that the strength and required light polarization of an excitonic optical transition are dictated by the optical matrix element winding number, a unique and heretofore unrecognized topological characteristic. We illustrate these findings in three gapped graphene systems – monolayer graphene with inequivalent sublattices and biased bi- and tri-layer graphene, where the pseudospin textures manifest into nontrivial optical matrix element winding numbers associated with different valley and photon circular polarization. This winding-number physics leads to novel exciton series and optical selection rules, with each valley hosting multiple bright excitons coupled to light of different circular polarization. This valley-exciton selective circular dichroism can be unambiguously detected using optical spectroscopy.

–

Presenters

  • Ting Cao

    University of California, Berkeley, Physics Department, UC Berkeley and Lawrence Berkeley National Lab, Physics, University of California - Berkeley

Authors

  • Ting Cao

    University of California, Berkeley, Physics Department, UC Berkeley and Lawrence Berkeley National Lab, Physics, University of California - Berkeley

  • Meng Wu

    Department of Physics, University of California at Berkeley and Materials Sciences Division, Lawrence Berkeley National Laboratory, Physics Department, University of California Berkeley and Lawrence Berkeley National Lab, Physics Department, UC Berkeley and Lawrence Berkeley National Lab

  • Steven Louie

    Physics, University of California, Berkeley, University of California, Berkeley, Physics, Univ of California - Berkeley, Univ of California - Berkeley, Physics, UC Berkeley, Physics Department, UC Berkeley and Lawrence Berkeley National Lab, Department of Physics, University of California at Berkeley and Materials Sciences Division, Lawrence Berkeley National Laboratory, Department of Physics, University of California, Berkeley, Physics Department, University of California Berkeley and Lawrence Berkeley National Lab, Department of physics, University of California - Berkeley, Lawrence Berkeley National Lab and University of California - Berkeley, Materials Sciences Division, Lawrence Berkeley National Laboratory & Department of Physics, University of California at Berkeley, UC Berkeley and Lawrence Berkeley National Lab, Physics, University of California - Berkeley