Experimental observation of coupled valley and spin Hall effect in p‐doped WSe₂ devices

Abstract

Giant spin Hall effect (GSHE) has been observed in heavy metal materials such as Ta, Pt, and W, where spins are polarized in the surface plane and perpendicular to the charge current direction 1-3 . Spins generated in these materials have successfully switched magnets with in-plane magnetic anisotropy (IMA) and perpendicular magnetic anisotropy (PMA) through spin orbit torque (SOT) mechanism. It is generally accepted that PMA magnets are preferred over IMA magnets in data storage applications owing to their large thermal stability even at ultra-scaled dimensions 4 .However, SOT switching of PMA magnets by conventional GSHE materials requires either a small external magnetic field 5,6 , a local dipolar field 7 , or introducing tilted anisotropy to break the symmetry with respect to the magnetization 8,9 . To deterministically switch a PMA without any additional assistance, nonconventional GSHE materials that can generate spins with polarization perpendicular to the surfaces are needed. Several monolayer transition metal dichalcogenides (TMDs) have been predicted to generate such out-of-plane spins due to their 2D nature and unique band structures 10-12 . Interestingly, opposite spins are locked to their respective sub-band in each K valley of the TMD valence band with substantially large energy splitting, which enables polarized spins to be accessible through electrical gating and spatially separated by electric field through the valley Hall effect (VHE) [13][14][15][16][17][18] . Therefore, spatial separation and accumulation of spins in these 2DTMDs are uniquely referred to as coupled valley and spin Hall effect 10 . Here, we report an experiment of electrical generation of spin current with out-of-plane polarization in monolayer WSe2 and detection of spin signals through a non-local spin valve structure built on a lateral graphene spin diffusion channel that partially overlaps with WSe2.

High-performance near-infrared Schottky-photodetector based graphene/In2S3 van der Waals heterostructures

“…Since the discovery of graphene, two-dimensional (2D) materials have demonstrated extremely impressive mechanical, electronic and optoelectronic properties of mechanical exibility, adjustable bandgap and strong light-matter interactions. [1][2][3][4][5][6][7][8][9][10][11][12][13] With the booming development of the 2D metal suldes, multiphase In 2 S 3 has attracted extensive attention and been used for high-performance applications in photodetectors, phase change memory devices and catalysis. [14][15][16][17] There are three main crystalline structures of a-In 2 S 3 , b-In 2 S 3 , and g-In 2 S 3 which have been reported.…”

Spin Torque Generated by Valley Hall Effect in WSe2

“…In these reports, an out-of-plane spin/valley polarization of 70% was observed at the edges of p-doped monolayer WSe 2 due to VHE [27]. A similar electrically generated interfacial spin polarization of 38% was also observed in WSe 2 /graphene heterostructure [23]. Spin-valley locked states in TMDs are also long-lived [28,29] with large out-of-plane spin diffusion lengths of hundreds of nanometers [25].…”

“…Spinresolved photoemission spectroscopy measurements have revealed valley-dependent out-of-plane spin polarized valence states in TMDs [18][19][20][21][22]. Subsequently, transport experiments unambiguously demonstrated that a flow of out-of-plane spins in WSe 2 monolayers can be electrically generated through the valley Hall effect (VHE) [23], a topological Hall response driven by the finite and opposite Berry curvatures in the two valleys [23][24][25][26][27]. In these reports, an out-of-plane spin/valley polarization of 70% was observed at the edges of p-doped monolayer WSe 2 due to VHE [27].…”

All-Electrical Control and Temperature Dependence of the Spin and Valley Hall Effect in Monolayer WSe2 Transistors

“…The intervalley scattering of holes in WSe 2 must also flip spin, resulting in a prolonged spin and valley lifetime . While all-electrical measurements of the spin or valley Hall effect have been performed at room temperature, − it is a challenge to distinguish the SVHE non-local electrical signal from other potential sources, including a variety of unclear effects that are unrelated to spin and valley, similar to those reported in previous works on graphene. − Optical measurements of electrically generated SVHE, on the other hand, can directly image the spatial distribution of the polarization and can be used to extract more parameters. Previous work has demonstrated, via spatial Kerr rotation (KR) measurements, the observation of the SVHE in n-type bilayer and monolayer MoS 2 and in p-type monolayer WSe 2 FETs at temperatures from 20 to 30 K. However, little work has shown electrical control of the SVHE, and detailed interpretation of the SVHE-induced KR data and the study of the temperature and carrier density dependence of SVHE parameters are sorely lacking.…”