Valley and spin dynamics in MoSe2 two-dimensional crystals

Abstract

We study valley and spin dynamics in monolayer molybdenum diselenide by polarization-resolved femtosecond transient absorption spectroscopy. Valley- and spin-polarized excitons are injected by a circularly polarized laser pulse, with an excess energy of 120 meV. Relaxation of the valley polarization is time-resolved by measuring dynamical circular dichroism of a linearly polarized probe pulse tuned to 790 nm, the peak of the exciton resonance of monolayer MoSe₂. We obtain a valley relaxation time of 9 ± 3 ps at room temperature, which is at least one order of magnitude shorter than the simultaneously measured exciton lifetime. The results illustrate potential applications of MoSe₂ in room-temperature valleytronic and spintronic devices.