Coherent spin dynamics of excitons in strained monolayer semiconductors

TL;DR

This paper models the coherent spin and valley dynamics of excitons in strained monolayer semiconductors, revealing how strain-induced effects influence exciton polarization oscillations and uncovering different dynamical regimes.

Contribution

It introduces a theoretical model describing how elastic strain affects exciton spin-valley coherence and polarization dynamics in 2D transition metal dichalcogenides.

Findings

Strain splits the exciton radiative doublet into linearly polarized states.

Oscillations in exciton circular polarization depend on strain and splitting effects.

Multiple frequencies appear in polarization beats under large strain conditions.

Abstract

We develop a model of the coherent exciton spin-valley dynamics in two-dimensional transition metal dichalcogenides under elastic strain. The strain splits the exciton radiative doublet in linearly polarized states. Consequently, it induces an effective magnetic field acting on the exciton pseudospin and causes its precession. As a result, under circularly polarized excitation, the circular polarization of excitons oscillates with time, also a time-oscillating linear polarization appears. We study competition of the strain-induced effective magnetic field with the field caused by the exciton longitudinal-transverse splitting. We uncover different regimes of coherent spin dynamics of two-dimensional excitons. In particular, we show that for sufficiently large strain-induced and longitudinal-transverse splittings two frequencies related to these splittings appear in the exciton circular polarization beats.