Inverted valley polarization in optically excited transition metal dichalcogenides
Journal article, 2018

Large spin-orbit coupling in combination with circular dichroism allows access to spin-polarized and valley-polarized states in a controlled way in transition metal dichalcogenides. The promising application in spin-valleytronics devices requires a thorough understanding of intervalley coupling mechanisms, which determine the lifetime of spin and valley polarizations. Here we present a joint theory-experiment study shedding light on the Dexter-like intervalley coupling. We reveal that this mechanism couples A and B excitonic states in different valleys, giving rise to an efficient intervalley transfer of coherent exciton populations. We demonstrate that the valley polarization vanishes and is even inverted for A excitons, when the B exciton is resonantly excited and vice versa. Our theoretical findings are supported by energy-resolved and valley-resolved pump-probe experiments and also provide an explanation for the recently measured up-conversion in photoluminescence. The gained insights might help to develop strategies to overcome the intrinsic limit for spin and valley polarizations.

Author

Gunnar Berghäuser

Chalmers, Physics, Condensed Matter Theory

Ivan Bernal

Chalmers, Physics, Condensed Matter Theory

Robert Schmidt

University of Münster

R. Schneider

University of Münster

Iris Niehues

University of Münster

Paul Erhart

Chalmers, Physics, Materials and Surface Theory

S. M. de Vasconcellos

University of Münster

R. Bratschitsch

University of Münster

A. Knorr

Technische Universität Berlin

Ermin Malic

Chalmers, Physics, Condensed Matter Theory

Nature Communications

2041-1723 (ISSN)

Vol. 9 1 971

Subject Categories

Atom and Molecular Physics and Optics

Other Physics Topics

Condensed Matter Physics

DOI

10.1038/s41467-018-03354-1

More information

Latest update

4/4/2018 9