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

TL;DR

This study demonstrates that mechanical bending in tungsten diselenide nanoribbons can tune spin polarization, excitonic states, and optical absorption, enabling potential applications in spintronics and quantum information devices.

Contribution

It reveals how bending induces anisotropic spin polarization and tunable excitonic properties in WSe₂ nanoribbons, combining first-principles calculations with many-body methods.

Findings

Enhanced spin-orbit coupling and spin polarization under bending.

Optical absorption tunable from 0.4 to 1.5 eV with bending.

Bending controls exciton spin configurations.

Abstract

A WSe$_2$ 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 WSe$_2$ nanoribbons under different mechanical bending curvatures and electron/hole doping with density functional theory and their optical absorption and excitonic states with many-body perturbation GW and BSE (Bethe-Salpeter equation) methods. We found that the WSe$_2$ nanoribbons can exhibit an enhanced SOC effect and a spatially varying spin polarization in bands around the Fermi level under bending. The spin-polarization can show an anisotropy (or asymmetry) in those nearly degenerate bands, leading to a controllable magnetism via bending and electron/hole doping to 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 at a large bending condition. The exciton states generally show mixed or various spin configuration in the electron and hole pairs that are controlled by bending, potentially useful for applications in spin-based quantum information processes.