# Persistent spin helix in Rashba-Dresselhaus ferroelectric CsBiNb2O7

## TL;DR

This paper demonstrates that CsBiNb2O7 is a ferroelectric Rashba semiconductor exhibiting a persistent spin helix, which could enable long spin lifetimes and advance spintronic device applications.

## Contribution

It identifies CsBiNb2O7 as a robust ferroelectric with reversible spin texture and potential for persistent spin helix, expanding the class of materials suitable for spintronics.

## Key findings

- CsBiNb2O7 exhibits strong Rashba spin splitting.
- The spin texture is reversible by electric field.
- Potential for long spin lifetime due to persistent spin helix.

## Abstract

Ferroelectric Rashba semiconductors (FERSC) are a novel class of multifunctional materials showing a giant Rashba spin splitting which can be reversed by switching the electric polarization. Although they are excellent candidates as channels in spin field effect transistors, the experimental research has been limited so far to semiconducting GeTe, in which ferroelectric switching is often prevented by heavy doping and/or large leakage currents. Here, we report that CsBiNb2O7, a layered perovskite of Dion-Jacobson type, is a robust ferroelectric with sufficiently strong spin-orbit coupling and spin texture reversible by electric field. Moreover, we reveal that its topmost valence band's spin texture is quasi-independent from the momentum, as a result of the low symmetry of its ferroelectric phase. The peculiar spin polarization pattern in the momentum space may yield the so-called "persistent spin helix", a specific spin-wave mode which protects the spin from decoherence in diffusive transport regime, potentially ensuring a very long spin lifetime in this material.