Ferroelectric nonlinear anomalous Hall effect in few-layer WTe$_2$

TL;DR

This paper demonstrates a ferroelectric nonlinear anomalous Hall effect in few-layer WTe₂, showing even-odd layer oscillations due to Berry curvature and shift dipole changes, opening new avenues in nonlinear quantum electronics.

Contribution

The study reveals the layer-dependent ferroelectric nonlinear anomalous Hall effect in WTe₂, linking it to Berry curvature and shift dipoles, and introduces these as new order parameters for noncentrosymmetric materials.

Findings

Odd-layer WTe₂ exhibits a switch in nonlinear Hall current upon ferroelectric transition.

Even-layer WTe₂ shows invariant nonlinear Hall current despite ferroelectric transition.

The effect originates from the reversal of Berry curvature and shift dipoles in different layers.

Abstract

Under broken time reversal symmetry such as in the presence of external magnetic field or internal magnetization, a transverse voltage can be established in materials perpendicular to both longitudinal current and applied magnetic field, known as classical Hall effect. However, this symmetry constraint can be relaxed in the nonlinear regime, thereby enabling nonlinear anomalous Hall current in time-reversal invariant materials - an underexplored realm with exciting new opportunities beyond classical linear Hall effect. Here, using group theory and first-principles theory, we demonstrate a remarkable ferroelectric nonlinear anomalous Hall effect in time-reversal invariant few-layer WTe$_2$ where nonlinear anomalous Hall current switches in odd-layer WTe$_2$ while remaining invariant in even-layer WTe$_2$ upon ferroelectric transition. This even-odd oscillation of ferroelectric nonlinear anomalous Hall effect was found to originate from the absence and presence of Berry curvature dipole reversal and shift dipole reversal due to distinct ferroelectric transformation in even and odd-layer WTe$_2$. Our work not only treats Berry curvature dipole and shift dipole on an equal footing to account for intraband and interband contributions to nonlinear anomalous Hall effect, but also establishes Berry curvature dipole and shift dipole as new order parameters for noncentrosymmetric materials. The present findings, therefore, suggest that ferroelectric metals and Weyl semimetals may offer unprecedented opportunities for the development of nonlinear quantum electronics.