Manipulation of room-temperature Valley-Coherent Exciton-Polaritons in atomically thin crystals by real and artificial magnetic fields

TL;DR

This study demonstrates that valley coherence in monolayer WSe2 can be observed and manipulated at room temperature using strong coupling with a microcavity and external magnetic fields, advancing valleytronics.

Contribution

It shows for the first time that valley coherence can be maintained and controlled at ambient conditions via cavity coupling and magnetic fields in atomically thin crystals.

Findings

Valley coherence observed at room temperature in WSe2 monolayers.

Magnetic fields and cavity polarization anisotropy can manipulate valley phase.

Model based on pseudospin rate equations agrees with experimental results.

Abstract

Strong spin-orbit coupling and inversion symmetry breaking in transition metal dichalcogenide monolayers yield the intriguing effects of valley-dependent optical selection rules. As such, it is possible to substantially polarize valley excitons with chiral light and furthermore create coherent superpositions of K and K- polarized states. Yet, at ambient conditions dephasing usually becomes too dominant, and valley coherence typically is not observable. Here, we demonstrate that valley coherence is, however, clearly observable for a single monolayer of WSe2, if it is strongly coupled to the optical mode of a high quality factor microcavity. The azimuthal vector, representing the phase of the valley coherent superposition, can be directly manipulated by applying magnetic fields, and furthermore, it sensibly reacts to the polarization anisotropy of the cavity which represents an artificial magnetic field. Our results are in qualitative and quantitative agreement with our model based on pseudospin rate equations, accounting for both effects of real and pseudo-magnetic fields.