Robust spin-valley polarization in commensurate MoS2 /graphene heterostructures

Abstract

The investigation and control of quantum degrees of freedom (DoF) of carriers lie at the heart of condensed-matter physics and next-generation electronics/optoelectronics. Van der Waals heterostructures stacked from distinct two-dimensional (2D) crystals offer an unprecedented platform for combining the superior properties of individual 2D materials and manipulating spin, layer and valley DoFs. MoS 2 /graphene heterostructures, harboring prominent spin transport properties of graphene, giant spin-orbit coupling and spin-valley polarization of MoS 2 , are predicted as a perfect venue for optospintronics. Here, we report the epitaxial growth of commensurate MoS 2 on graphene with high-quality by chemical vapor deposition, and demonstrate robust temperature-independent spin-valley polarization at off-resonant excitation for the first time. We further show that the helicity of B exciton is larger than that of A exciton, allowing the manipulation of spin bits in the commensurate

Synthesis and characterization of WS2/graphene/SiC van der Waals heterostructures via WO3−x thin film sulfurization

“…In addition, spin polarization in TMDs is complemented by long spin lifetimes in graphene 9 , 10 . When combined in a heterostructure these two materials can deliver outstanding performance in a range of applications including optoelectronics 11 – 13 , spintronics and valleytronics 14 – 16 , sensing 17 , 18 , and energy storage 19 , 20 .…”

Engineering Valley Polarization of Monolayer WS2: A Physical Doping Approach

“…However, the reported values of P c in monolayer TMDs vary from 2% to nearly 100% among different TMD semiconductors, which are mainly attributed to intervalley scattering process from the selectively pumped valley to the opposite one . As for the PL measurements, various approaches have been adopted to obtain a sizable P c like applying magnetic field, cooling down to liquid helium cryogenic temperature, using near resonant light excitation or building van der Waals heterostructure . More practical and desirable methods could be electrical and optical control of valley polarization in TMDs at noncryogenic temperature and off‐resonance conditions.…”

Robust circular polarization of indirect Q-K transitions in bilayer 3R−WS2

“…It is highly desired to quest for a system manifesting robust CP. Due to the combination of time-reversal symmetry and explicitly broken spatial-inversion symmetry, K and K valleys of monolayer transition-metal dichalcogenides (TMDCs) enable contrasting Berry curvature and magnetic moment, giving rise to valleyselective CP of direct excitons at the corners of a hexagonal Brillouin zone [9][10][11][12][13][14][15]. Besides K valleys, six nonequivalent Q pockets related by both threefold rotational symmetry and time-reversal symmetry are also the critical points of the conduction band (CB) [16][17][18].…”

“…The error bar stems from multiple measurements of at least three samples. [12,15,33]. Due to the conservation of lattice momentum for optical transitions, τ E of the direct excitons is much shorter than that of the indirect excitons.…”