Transition from Optically Excited to Intrinsic Spin Polarization in WSe$_2$

TL;DR

This study explores how spin polarization in bulk WSe$_2$ transitions from optically excited states to intrinsic conduction band states, revealing the timescale and mechanisms of spin dynamics relevant for spintronic applications.

Contribution

It provides the first detailed investigation of the transition from optically excited to intrinsic spin polarization in WSe$_2$ using advanced spin-resolved spectroscopy.

Findings

Spin-conserving intervalley scattering observed.

Transition to intrinsic spin polarization occurs after approximately 150 fs.

Time-resolved measurements track the evolution of spin carriers.

Abstract

Layered 2D van der Waals materials, such as transition metal dichalcogenides, are promising for nanoscale spintronic and optoelectronic applications. Harnessing their full potential requires understanding both intrinsic transport and the dynamics of optically excited spin and charge carriers -- particularly the transition between excited spin polarization and the conduction band's intrinsic spin texture. Here, we investigate the spin polarization of the conduction bands of bulk WSe$_2$ using static and time-resolved spin-resolved photoemission spectroscopy, complemented by photocurrent calculations. Electron doping reveals the intrinsic spin polarization, while time-resolved measurements trace the evolution of excited spin carriers. We find that intervalley scattering is spin-conserving, with spin transport initially governed by photoexcited carriers and aligning with the intrinsic conduction band polarization after $\sim$150 fs.