Doping Dependence of Spin-Momentum Locking in Bismuth-Based High-Temperature Cuprate Superconductors

TL;DR

This study investigates how spin-momentum locking varies with doping in bismuth-based cuprate superconductors, revealing a momentum-dependent spin texture that may be linked to local structural fluctuations affecting superconductivity.

Contribution

It provides the first detailed momentum-resolved analysis of spin textures across the doping phase diagram in cuprates, highlighting the role of local inversion symmetry breaking.

Findings

Spin polarization varies with doping and diminishes with lead substitution.

A universal spin texture is observed across different cuprate samples.

Local structural fluctuations may induce inversion symmetry breaking and spin polarization.

Abstract

Non-zero spin orbit coupling has been reported in several unconventional superconductors due to the absence of inversion symmetry breaking. This contrasts with cuprate superconductors, where such interaction has been neglected for a long time. The recent report of a non-trivial spin orbit coupling in overdoped Bi2212 cuprate superconductor, has re-opened an old debate on both the source and role of such interaction and its evolution throughout the superconducting dome. Using high-resolution spin- and angle-resolved photoemission spectroscopy, we reveal a momentum-dependent spin texture throughout the hole-doped side of the superconducting phase diagram for single- and double-layer bismuth-based cuprates. The universality of the reported effect among different dopings and the disappearance of spin polarization upon lead substitution, suggest a common source. We argue that local structural fluctuations of the CuO planes and the resulting charge imbalance may cause local inversion symmetry breaking and spin polarization, which might be crucial for understanding cuprates physics.