Imaging spin dynamics in monolayer WS ₂ by time-resolved Kerr rotation microscopy

Abstract

Monolayer transition metal dichalcogenides (TMD) have immense potential for future spintronic and valleytronic applications due to their 2D nature and long spin/valley lifetimes. We investigate the origin of these long-lived states in n-type WS2 using time-resolved Kerr rotation microscopy and photoluminescence microscopy with ~1 µm spatial resolution. Comparing the spatial dependence of the Kerr rotation signal and the photoluminescence reveals a correlation with neutral exciton emission, which is likely due to the transfer of angular momentum to resident conduction electrons with long spin/valley lifetimes. In addition, we observe an unexpected anticorrelation between the Kerr rotation and trion emission, which provides evidence for the presence of long-lived spin/valley-polarized dark trions. We also find that the spin/valley polarization in WS2 is robust to magnetic fields up to 700 mT, indicative of spins and valleys that are stabilized with strong spin–orbit fields.

Spin-phonon relaxation from a universal ab initio density-matrix approach

“…This is because large SOC splitting at the valence band maximum makes the intravalley transition between two valence bands nearly impossible based on energy conservation in the electron-phonon scattering process. Experimental measurements also observe long spin relaxation times dominated by intervalley scattering in tungsten dichalcogenides 44 , which may facilitate applications in spintronic and valleytronic devices.…”

Hyperfine interaction in atomically thin transition metal dichalcogenides

“…For resident charge carriers this limitation is released. The polarization can be preserved for a few nanoseconds in MoS 2 [45][46][47], and even longer in WSe 2 [48][49][50]. Particularly long polarization relaxation times can be obtained for the localized * smirnov@mail.ioffe.ru charge carriers, where the dominant role in the spin and valley dynamics is played by the hyperfine interaction with the host lattice nuclear spins [28,51].…”

Spin Accumulation and Dynamics in Inversion-Symmetric van der Waals Crystals

“…Different studies in the literature show competing results on the effect of an in-plane magnetic field on the spin relaxation in monolayer TMDs. While a few studies show that a small magnetic field has no effect on the total spin-valley accumulation [13,26,29,31] as expected from the large spin-orbit fields (B SO ) in TMDs, other works show an increase [25] or decrease on the spin signal and even coherent precession in their signals [23,30], which has been attributed to spins in localized defects. It has been proposed that the fast decay of TRKR signals with µ 0 H y in TMD monolayers could be due to an enhanced inter-valley scattering [23].…”