Spin-polarization anisotropy controlled by bending in tungsten diselenide nanoribbons and tunable excitonic states

Abstract

A WSe₂ monolayer shows many interesting properties due to its spin–orbit coupling induced spin splitting in bands around the Fermi level and the spin–valley configuration. The orientation of the spin-polarization in the relevant bands is crucial for the nature of exciton states and the optical valley selectivity. In this work, we studied the electronic properties of the WSe₂ nanoribbons under different mechanical bending curvatures and electron/hole doping using density functional theory and their optical absorption and excitonic states using many-body perturbation GW and BSE (Bethe–Salpeter equation) methods. We found that the WSe₂ nanoribbons can exhibit an enhanced SOC effect and a spatially varying spin-polarization in bands around the Fermi level under bending conditions. The spin-polarization can show an anisotropy (or asymmetry) in these nearly degenerate bands, leading to a controllable magnetism via bending and electron/hole doping of the nanoribbons, suggesting a potential application in compact and controllable magnetic nanodevices and spintronics. The optical absorption spectrum of the nanoribbon presents a large tunability with bending within the near infrared region of about 0.4 to 1.5 eV, showing an enhanced absorption under a large bending condition. The exciton states generally show mixed or various spin configurations in the electron and hole pairs that are controlled by bending, potentially useful for applications in spin-based quantum information processes.