Magnetically-Sensitive Valley Polarization Reversal and Revival of Defect-Localized Excitons in WSe2-WS2

TL;DR

This study demonstrates magnetic field control over valley polarization in defect-localized excitons within WSe2-WS2 heterobilayers, revealing reversal and revival phenomena that enhance understanding of valley dynamics in TMDs.

Contribution

It uncovers magnetic field-induced reversal and revival of valley polarization in defect-localized excitons, a novel control mechanism in TMD heterostructures.

Findings

Valley polarization can be reversed by weak magnetic fields in interlayer defect excitons.

Valley polarization can be revived after decay in intralayer defect excitons under moderate magnetic fields.

Defect-localized excitons exhibit microsecond lifetimes, enabling magnetic manipulation.

Abstract

Manipulating and reserving the valley pseudospin of excitons is one core aim in the two-dimensional transition metal dichalcogenides (TMDs). However, due to the strong electron-hole exchange and spin-orbit coupling interactions, the exciton recombination lifetime is subject to picosecond timescale intrinsically, and the valley polarization is hardly modulated by a moderate magnetic field. It is fortunate that interlayer and defect-localized excitons promise to overcome these difficulties by suppressing the above interactions. Here we clearly reveal that the valley polarization can be reversed and revived in the defect-localized excitons with a microsecond lifetime in AB-stacked WSe2-WS2 heterobilayer. Specifically, for the interlayer defect-localized exciton, the valley polarization is reversed and can be efficiently enhanced by a weak out-of-plane magnetic field (<0.4 T). In sharp contrast, the valley polarization of the intralayer defect-localized exciton can revive after a fast decay process and follows the direction of the moderate out-of-plane magnetic field (<3 T). We explain the reversed valley polarization with highly magnetic sensitivity by the delocalization of defect-localized holes under a weak magnetic field and the revival of valley polarization by the valley Zeeman effect under a moderate magnetic field. Our results demonstrate that the valley pseudospin of defect-localized excitons can be efficiently modulated by the external magnetic field and enrich both the understanding and the technical approaches on manipulating the valley dynamics in TMDs and their heterostructure.