Magneto-optical Kerr spectroscopy of spin-valley polarization in gate-tunable suspended WSe2 monolayers

Haruki Sanada,
NTT Basic Research Laboratories

Abstract

Transition-metal dichalcogenides (TMDs) monolayers have attracted attention as a platform for hybridizing spintronics, valleytronics, and optoelectronics because of their optically accessible characteristic electronic structures coupled with spin and valley degrees of freedom. Suspending such monolayers on patterned substrates enables us to avoid local impurities and interfacial inhomogeneous strain due to the contact of the monolayer and substrates, allowing us to expect better electrical and optical properties. The suspended monolayers have been studied mainly by photoluminescence (PL) spectroscopy, which limits the analysis to short-lived (~ps) radiative excitons. Here, we employed pump-probe Kerr rotation (KR) spectroscopy to investigate the dynamics of the spin-valley polarization with longer lifetime (> ns) generated in a suspended WSe2 monolayer. The KR dynamics significantly depends on the back gate voltage and the probe wavelength, which provides a clue for a deeper understanding of origin of the spin valley polarization. The results indicate that our approach using the KR measurements on gate-tunable suspended TMD monolayers provides multiple tuning knobs for monitoring and controlling the spin-valley states of the exciton complexes in a single sample.