Signature of current-induced nuclear spin polarization in (Bi$_{1-x}$Sb$_{x}$)$_2$Te$_3$

TL;DR

This paper demonstrates current-induced nuclear spin polarization in a topological insulator, evidenced by an in-plane magnetic field offset affecting magnetoresistance, advancing understanding of spin interactions in such materials.

Contribution

It provides experimental evidence of nuclear polarization caused by electrical current in a topological insulator, linking spin-momentum locking to nuclear spin dynamics.

Findings

Measured in-plane magnetic field offset in sttight

Compared the offset to the Overhauser field magnitude

Attributed the offset to current-induced nuclear polarization

Abstract

In systems with spin-momentum locking, such as the surface states of three-dimensional topological insulators, a charge current is spin-polarized and spin-flip interactions between electron and nuclear spins can transfer this polarization to the nuclear spin system. When a nonzero bias voltage is applied, the nuclear polarization reaches a steady-state value. This polarization emerges as an effective in-plane magnetic field acting on electrons, called the Overhauser field, which causes an offset in-plane magnetoresistance perpendicular to the current, visible in experiments. The in-plane offset is measured in the three-dimensional topological insulator \bsttight, and the magnitude of the magnetic field offset is compared to the Overhauser field. We attribute the observed magnetic field offset to current-induced nuclear polarization in \bsttight, which forms an important step towards experimentally realizing an entropic inductor.