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

Ting Cao, Meng Wu, and Steven G. Louie
Phys. Rev. Lett. 120, 087402 – Published 23 February 2018
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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 multicomponent 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 trilayer 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.

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  • Received 31 July 2017
  • Revised 3 October 2017

DOI:https://doi.org/10.1103/PhysRevLett.120.087402

© 2018 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Ting Cao, Meng Wu, and Steven G. Louie*

  • Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

  • *sglouie@berkeley.edu

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Issue

Vol. 120, Iss. 8 — 23 February 2018

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