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Register a new userSpin diffusion in p-type bilayer WSe$_2$
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We investigate the steady-state out-of-plane spin diffusion in p-type bilayer WSe2 in the presence of the Rashba spin-orbit coupling and Hartree-Fock effective magnetic field. The out-of-plane components of the Rashba spin-orbit coupling serve as the opposite Zeeman-like fields in the two valleys. Together with the identical Hartree-Fock effective magnetic fields, different total effective magnetic field strengths in the two valleys are obtained. It is further revealed that due to the valley-dependent total effective magnetic field strength, similar (different) spin-diffusion lengths in the two valleys are observed at small (large) spin injection. Nevertheless, it is shown that the intervalley hole-phonon scattering can suppress the difference in the spin-diffusion lengths at large spin injection due to the spin-conserving intervalley charge transfers with the opposite transfer directions between spin-up and -down holes. Moreover, with a fixed large pure spin injection, we predict the build-up of a steady-state valley polarization during the spin diffusion with the maximum along the diffusion direction being capable of exceeding 1 %. It is revealed that the valley polarization arises from the induced quasi hot-hole Fermi distributions with different effective hot-hole temperatures between spin-up and -down holes during the spin diffusion, leading to the different intervalley charge transfer rates in the opposite transfer directions. Additionally, it is also shown that by increasing the injected spin polarization, the hole density or the impurity density, the larger valley polarization can be obtained.
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Spin-orbit coupling in graphene can be increased far beyond its intrinsic value by proximity coupling to a transition metal dichalcogenide. In bilayer graphene, this effect was predicted to depend on the occupancy of both graphene layers, rendering it gate-tunable by an out-of-plane electric field. We experimentally confirm this prediction by studying magnetotransport in a dual-gated WSe$_2$/bilayer graphene heterostructure. Weak antilocalization, which is characteristic for phase-coherent transport in diffusive samples with spin-orbit interaction, can be strongly enhanced or suppressed at constant carrier density, depending on the polarity of the electric field. From the spin-orbit scattering times extracted from the fits, we calculate the corresponding Rashba and intrinsic spin-orbit parameters. They show a strong dependence on the transverse electric field, which is well described by a gate-dependent layer polarization of bilayer graphene.
We report scanning tunneling microscopy (STM) and spectroscopy (STS) measurements of monolayer and bilayer WSe$_2$. We measure a band gap of 2.21 $pm$ 0.08 eV in monolayer WSe$_2$, which is much larger than the energy of the photoluminescence peak indicating a large excitonic binding energy. We additionally observe significant electronic scattering arising from atomic-scale defects. Using Fourier transform STS (FT-STS), we map the energy versus momentum dispersion relations for monolayer and bilayer WSe$_2$. Further, by tracking allowed and forbidden scattering channels as a function of energy we infer the spin texture of both the conduction and valence bands. We observe a large spin-splitting of the valence band due to strong spin-orbit coupling, and additionally observe spin-valley-layer coupling in the conduction band of bilayer WSe$_2$.
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