Modulating spin-valley relaxation in WSe$_2$ with variable thickness VOPc layers

TL;DR

This study investigates how varying the thickness of VOPc molecular layers on WSe$_2$ influences spin-valley relaxation, revealing that thicker layers enhance polarization lifetime by modifying interfacial interactions.

Contribution

It demonstrates the impact of molecular layer thickness on spin-valley dynamics at TMDC/molecular interfaces, a novel insight into interface engineering for quantum information applications.

Findings

Thinnest VOPc layer destroys spin-valley polarization rapidly.

Thicker VOPc layers extend spin-valley polarization lifetime.

Interfacial states and exchange interactions are key to relaxation mechanisms.

Abstract

Combining the synthetic tunability of molecular compounds with the optical selection rules of transition metal dichalcogenides (TMDC) that derive from spin-valley coupling could provide interesting opportunities for the readout of quantum information. However, little is known about the electronic and spin interactions at such interfaces and the influence on spin-valley relaxation. In this work, vanadyl phthalocyanine (VOPc) molecular layers are thermally evaporated on WSe$_2$ to explore the effect of molecular layer thickness on excited-state spin-valley polarization. The thinnest molecular layer supports an interfacial state which destroys the spin-valley polarization almost instantaneously, whereas a thicker molecular layer results in longer-lived spin-valley polarization than the WSe$_2$ monolayer alone. The mechanism appears to involve a tightly-bound species at the molecule/TMDC interface that strengthens exchange interactions and is largely avoided in thicker VOPc layers that isolate electrons from WSe$_2$ holes.