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Phys Rev Lett. 2015 Oct 30;115(18):187002. doi: 10.1103/PhysRevLett.115.187002. Epub 2015 Oct 30.

Anomalous Light Cones and Valley Optical Selection Rules of Interlayer Excitons in Twisted Heterobilayers.

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Department of Physics and Center of Theoretical and Computational Physics, The University of Hong Kong, Hong Kong, China.
Department of Physics, University of Washington, Seattle, Washington 98195, USA.
Department of Materials Science and Engineering, University of Washington, Seattle, Washington 98195, USA.


We show that, because of the inevitable twist and lattice mismatch in heterobilayers of transition metal dichalcogenides, interlayer excitons have sixfold degenerate light cones anomalously located at finite velocities on the parabolic energy dispersion. The photon emissions at each light cone are elliptically polarized, with the major axis locked to the direction of exciton velocity, and helicity specified by the valley indices of the electron and the hole. These finite-velocity light cones allow unprecedented possibilities for optically injecting valley polarization and valley current, and the observation of both direct and inverse valley Hall effects, by exciting interlayer excitons. Our findings suggest potential excitonic circuits with valley functionalities, and unique opportunities to study exciton dynamics and condensation phenomena in semiconducting 2D heterostructures.

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