Abstract
Valley pseudospin, a novel quantum degree of freedom, is expected to show valley Zeeman effect in analogy to real spin in magnetic field B. By performing first-principles calculations, we studied the magnetic effect on valley pseudospin in monolayer WSe2. With the application of B, the time reversal symmetry is broken. Our calculation shows that the valley energy degeneracy is broken and the valley Zeeman splitting varies linearly with B, agreeing well with the experiments. It is found that the valley Zeeman splitting is contributed mainly from the atomic orbital magnetic moment of W atom, but the valley contribution is still appreciable. The Berry curvatures of the two inequivalent valleys of monolayer WSe2 are opposite and their change induced by B also depends linearly on B. The calculated circular dichroism and dielectric function reveal that the optical valley-dependent selection rule is preserved and the original single peak in polarization-resolved photoluminescence spectrum will be split into two peaks after the application of B. Our studies demonstrate the possibility of magnetic manipulation of the valley pseudospin.
Highlights
Valley pseudospin is a novel quantum degree of freedom of electrons in solids analogous to spin, which corresponds to the states near the energy extrema in electronic bands of solids.1,2 Since inequivalent valleys have opposite electrical, magnetic and optical properties, valleytronics is very promising in applications of information processing and storage.3,4 Transition metal dichalcogenide (TMD) monolayer MX2 such as e.g., MoS2, WSe2 are excellent valleytronic materials under intensive exploration.5,6 The honeycomb TMD monolayer has a central transition metal atom layer between two chalcogen atom layers
spin-orbit coupling (SOC) leads to giant spin splitting in valence band maximum (VBM), but a much smaller one in conduction band minimum (CBM)
The valleytronics of WSe2 monolayer in external magnetic field has been studied by first-principles calculations
Summary
Valley pseudospin is a novel quantum degree of freedom of electrons in solids analogous to spin, which corresponds to the states near the energy extrema in electronic bands of solids. Since inequivalent valleys have opposite electrical, magnetic and optical properties, valleytronics is very promising in applications of information processing and storage. Transition metal dichalcogenide (TMD) monolayer MX2 such as e.g., MoS2, WSe2 are excellent valleytronic materials under intensive exploration. The honeycomb TMD monolayer has a central transition metal atom layer between two chalcogen atom layers. Since inequivalent valleys have opposite electrical, magnetic and optical properties, valleytronics is very promising in applications of information processing and storage.. Transition metal dichalcogenide (TMD) monolayer MX2 such as e.g., MoS2, WSe2 are excellent valleytronic materials under intensive exploration.. Mo and W atoms in MX2 are nonmagnetic and the time reversal symmetry is preserved. Owing to spatial inversion asymmetry of TMD monolayer and time reversal symmetry, the Dirac valleys have valley-contrasting Berry curvatures, which underlies the fascinating Berry phase related quantum effects such as valley Hall effect, valley contrasting magnetic moments and valley dependent circular dichroism.. Time reversal symmetry mandates opposite spin-splittings at ±K valleys, and there is valley-spin coupling in TMDs. The two inequivalent Dirac valleys have opposite orbital and spin magnetic moments, suggesting a route to magnetic manipulation of valley pseudospins
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