Spin-Valley Relaxation of Rydberg Excitons

TL;DR

This study measures spin relaxation times of Rydberg excitons in WSe2 monolayers, revealing a significant increase with quantum number and demonstrating tunable spin-valley dynamics in 2D semiconductors.

Contribution

It provides the first direct measurement of spin relaxation times for Rydberg excitons and introduces a microscopic model explaining their spin dynamics.

Findings

Spin relaxation time increases from ~2 ps (1s) to ~75 ps (3s) excitons.

Photoluminescence circular polarization approaches 90% for the 3s state.

Microscopic model reproduces the observed trend based on electron-hole exchange.

Abstract

Rydberg excitons, characterized by large spatial extension and reduced electron-hole overlap, must have a spin-valley dynamics different from that of ground state excitons. Here we report a direct measurement of spin relaxation of Rydberg excitons in high-quality WSe2 monolayer using continuous-wave and time-resolved optical orientation experiments. Excited excitonic states exhibit exceptionally large photoluminescence circular polarization, approaching 90% for the 3s state. Time-resolved measurements reveal a strong increase of the spin relaxation time with the principal quantum number, from ~2 ps for the 1s exciton to ~75 ps for the 3s exciton. A microscopic model based on electron-hole exchange-driven spin relaxation quantitatively reproduces the observed trend, demonstrating that Rydberg excitons enable tunable spin-valley dynamics in two-dimensional semiconductors.