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.

*This work is supported by DOE under Contract No. DE-AC02-05CH11231 and NSF Grant No. DMR-1508412, and computational resources from NERSC and XSEDE.

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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