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Chris Ciccarino1 2 Thomas Christensen3 Ravishankar Sundararaman4 Prineha Narang1

1, John A. Pauslon School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
2, Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States
3, Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
4, Department of Materials Science and Engineering, Rennnselaer Polytechnic Institute, Troy, New York, United States

Monolayer transition metal dichalcogenides have been the primary materials of interest in the field of valleytronics for their potential in information storage, yet the limiting factor has been achieving long valley decoherence times. We explore the dynamics of four monolayer TMDCs (MoS2 , MoSe2 , WS2 , WSe2) by describing electron-electron and electron-phonon interactions from first principles. We isolate the crucial impact of spin-orbit coupling on transport properties by comparing calculations which both omit and include relativistic effects. Spin-orbit coupling is found to increase carrier lifetimes at the valence band edge by over an order of magnitude, with a corresponding rise in hole mobility. This drastic change is attributed to spin-valley coupling. At temperatures of 50 K, we find valley coherence times on the order of 100 ps, with a maximum value of ~140 ps in WSe2. Our results capture the entangled relationship between spin and valley degrees of freedom, which is critical for valleytronic applications. Further, our work points towards interesting quantum properties on-demand in transition metal dichalcogenides that could be leveraged via driving spin, valley and phonon degrees of freedom.

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