Imaging of pure spin-valley diffusion current in WS ₂ -WSe ₂ heterostructures

Abstract

Transition metal dichalcogenide (TMDC) materials are promising for spintronic and valleytronic applications because valley-polarized excitations can be generated and manipulated with circularly polarized photons and the valley and spin degrees of freedom are locked by strong spin-orbital interactions. In this study we demonstrate efficient generation of a pure and locked spin-valley diffusion current in tungsten disulfide (WS)-tungsten diselenide (WSe) heterostructures without any driving electric field. We imaged the propagation of valley current in real time and space by pump-probe spectroscopy. The valley current in the heterostructures can live for more than 20 microseconds and propagate over 20 micrometers; both the lifetime and the diffusion length can be controlled through electrostatic gating. The high-efficiency and electric-field-free generation of a locked spin-valley current in TMDC heterostructures holds promise for applications in spin and valley devices.

A Facile and Effective Method for Patching Sulfur Vacancies of WS2 via Nitrogen Plasma Treatment

“…High‐performance transistors can be used in a variety of leading‐edge cross‐cutting fields, such as biosensors and artificial intelligence . The importance of obtaining high‐performance field‐effect transistors (FETs) motivates the search for new materials . Due to unique optoelectronic, electronic and chemical properties, transition metal dichalcogenides (TMDs) are attractive for use in the next‐generation high‐performance nanoelectronic era and substantial advancements in this field have been witnessed in the last several decades .…”

Mott and generalized Wigner crystal states in WSe2/WS2 moiré superlattices

“…Here we directly measure the doping-dependent decay of a pure spin excitation by taking advantage of the unique spin-valley selection rules in the TMDC heterostructure[10][11][12] . We use the pump-probe scheme described in Ref 25,26. to generate and probe the spin excitation in the moiré heterostructure.…”

Excitons in Two-Dimensional Materials

“…In contrast to the ultrafast charge transfer dynamics in vdWHs (<1ps), spin and valley relaxation dynamics take place on considerably longer timescale [68,69]. For the two distinctive relaxation processes in vdWHs (i.e., the population decay of optically excited excitons, and the exciton spin-valley lifetime which determines the information storage time in the spin-valley degree of freedom), they both are significantly longer than the monolayer case.…”

“…For the two distinctive relaxation processes in vdWHs (i.e., the population decay of optically excited excitons, and the exciton spin-valley lifetime which determines the information storage time in the spin-valley degree of freedom), they both are significantly longer than the monolayer case. For instance, by tuning the carrier concentration, holes' spin-valley lifetime and population lifetime possess a doping-dependent pattern in a WSe2/WS2 heterostructure [69]: in charge-neutral and electron-doped heterostructures (i.e., neutral and positive carrier concentrations), the spin-valley lifetime is closed to the population lifetime; nevertheless, in hole-doping heterostructures (i.e., negative carrier concentration), the spin-valley lifetime becomes orders of magnitude longer than the population lifetime ( Figure 7c). The remarkable dynamics of doping-dependent lifetime attributes to the distinctive interlayer electron-hole recombination process in the heterostructure, as shown in Figure 7c.…”