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

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.

Authors:
; ;
Publication Date:
Research Org.:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
Sponsoring Org.:
USDOE
OSTI Identifier:
1544322
Resource Type:
Journal Article
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 120; Journal Issue: 8; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English

Citation Formats

Cao, Ting, Wu, Meng, and Louie, Steven G. Unifying Optical Selection Rules for Excitons in Two Dimensions: Band Topology and Winding Numbers. United States: N. p., 2018. Web. doi:10.1103/PhysRevLett.120.087402.
Cao, Ting, Wu, Meng, & Louie, Steven G. Unifying Optical Selection Rules for Excitons in Two Dimensions: Band Topology and Winding Numbers. United States. doi:10.1103/PhysRevLett.120.087402.
Cao, Ting, Wu, Meng, and Louie, Steven G. Thu . "Unifying Optical Selection Rules for Excitons in Two Dimensions: Band Topology and Winding Numbers". United States. doi:10.1103/PhysRevLett.120.087402.
@article{osti_1544322,
title = {Unifying Optical Selection Rules for Excitons in Two Dimensions: Band Topology and Winding Numbers},
author = {Cao, Ting and Wu, Meng and Louie, Steven G.},
abstractNote = {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.},
doi = {10.1103/PhysRevLett.120.087402},
journal = {Physical Review Letters},
issn = {0031-9007},
number = 8,
volume = 120,
place = {United States},
year = {2018},
month = {2}
}

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