# Nonlinear planar Hall effect

## TL;DR

This paper reports the discovery of a nonlinear planar Hall effect in 3D topological insulator Bi2Se3 films, revealing a new spin-charge conversion mechanism linked to spin-momentum locking and symmetry breaking.

## Contribution

It introduces a novel nonlinear planar Hall effect in topological insulators, expanding understanding of spin-charge conversion phenomena in quantum materials.

## Key findings

- Hall resistance scales linearly with electric and magnetic fields
- Exhibits a {c6}/2 angle offset, different from conventional effects
- Originates from nonlinear spin current to charge current conversion

## Abstract

An intriguing property of three-dimensional (3D) topological insulator (TI) is the existence of surface states with spin-momentum locking, which offers a new frontier of exploration in spintronics. Here, we report the observation of a new type of Hall effect in a 3D TI Bi2Se3 film. The Hall resistance scales linearly with both the applied electric and magnetic fields and exhibits a {\pi}/2 angle offset with respect to its longitudinal counterpart, in contrast to the usual angle offset of {\pi}/4 between the linear planar Hall effect and the anisotropic magnetoresistance. This novel nonlinear planar Hall effect originates from the conversion of a nonlinear transverse spin current to a charge current due to the concerted actions of spin-momentum locking and time reversal symmetry breaking, which also exists in a wide class of non-centrosymmetric materials with a large span of magnitude. It provides a new way to characterize and utilize the nonlinear spin-to-charge conversion in a variety of topological quantum materials.

---
Source: https://tomesphere.com/paper/1906.06462