Room-temperature manipulation and processing of information encoded in the electronic valley pseudospin and spin degrees of freedoms lie at the heart of the next technological quantum revolution. In atomically thin layers of transition-metal dichalcogenides (TMDs) with hexagonal lattices, valley-polarized excitations and valley quantum coherence can be generated by simply shining with adequately polarized light. In turn, the polarization states of light can induce topological Hall currents in the absence of an external magnetic field, which underlies the fundamental principle of opto-valleytronics devices. However, demonstration of optical generation of valley polarization at room temperature has remained challenging and not well understood. Here, we demonstrate control of strong valley polarization (valley quantum coherence) at room temperature of up to ∼50% (∼20%) by strategically designing Coulomb forces and spin−orbit interactions in atomically thin TMDs via chalcogenide alloying. We show that tailor making the carrier density and the relative order between optically active (bright) and forbidden (dark) states by key variations on the chalcogenide atom ratio allows full control of valley pseudospin dynamics. Our findings set a comprehensive approach for intrinsic and efficient manipulation of valley pseudospin and spin degree of freedom toward realistic opto-valleytronics devices.
|Original language||English (US)|
|State||Published - Jul 31 2020|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: Q.X. gratefully acknowledges financial support from Singapore Ministry of Education via AcRF Tier3 Programme “Geometrical Quantum Materials” (MOE2018-T3-1-002) and two Tier1 grants (RG 113/16 and RG 194/17). W.Y. acknowledge support by RGC of HKSAR (C7036-17W) and the Croucher Foundation. Y.Z. acknowledges financial support from National Natural Science Foundation of China (Grant No.
21771161) and the Thousand Talents Program for Distinguished Young Scholars. H.Z. is thankful for the financial support from ITC via Hong Kong Branch of National Precious Metals Material Engineering Research Centre (NPMM) and the start-up grant (Project No. 9380100) and grants (Project Nos. 9610478 and 1886921) from the City University of Hong Kong. A.G.D.A. acknowledges Dr. Alexandra Álvarez Fernan- ́dez for useful discussions. A.G.D.A. gratefully acknowledges the financial support of the Presidential Postdoctoral Fellowship program of the Nanyang Technological University Singapore.