Fluctuated spin-orbital texture of Rashba-split surface states in real and reciprocal space

TL;DR

This study reveals complex, fluctuating spin-orbital textures in Rashba-split surface states, challenging simplified models and suggesting new possibilities for spin manipulation in spintronic applications.

Contribution

It demonstrates the unexpected variability and reversal of spin polarization in Rashba surface states through experimental and theoretical analysis.

Findings

Spin polarization varies and reverses with wavenumber.

Spin directions of Bi chains change from parallel to anti-parallel.

Results challenge the simplified Rashba model assumptions.

Abstract

Spin-orbit interaction (SOI) in low-dimensional systems, namely Rashba systems and the edge states of topological materials, is extensively studied in this decade as a promising source to realize various fascinating spintronic phenomena, such as the source of the spin current and spin-mediated energy conversion. Here, we show the odd fluctuation in the spin-orbital texture in a surface Rashba system on Bi/InAs(110)-(2$\times$1) by spin- and angle-resolved photoelectron spectroscopy and a numerical simulation based on a density-functional theory (DFT) calculation. The surface state shows a paired parabolic dispersion with the spin degeneracy lifted by the Rashba effect. Although its spin polarization should be fixed in a particular direction based on the Rashba model, the observed spin polarization varies greatly and even reverses its sign depending on the wavenumber. DFT calculations also reveal that the spin directions of two inequivalent Bi chains on the surface change from nearly parallel (canted-parallel) to anti-parallel in real space in the corresponding wavevector region. These results point out an oversimplification of the nature of spin in Rashba and Dirac systems and provide more freedom than expected for spin manipulation of photoelectrons.