Current-induced control of the polarization state in a polar metal based heterostructure SnSe/WTe$_2$

TL;DR

This study demonstrates current-induced polarization control in a SnSe/WTe$_2$ heterostructure, revealing interface-driven polarization switching and conductance changes in a polar metal-based system.

Contribution

We experimentally show how electric current can manipulate polarization states at the interface of a polar metal heterostructure, a novel approach in ferroelectric device control.

Findings

Sharp conductance drops at threshold voltages

Gate voltage influences threshold positions

Re-entrant low-conductance transition observed

Abstract

The concept of a polar metal proposes new approach of current-induced polarization control for ferroelectrics. We fabricate SnSe/WTe$_2$ heterostructure to experimentally investigate charge transport between two ferroelectric van der Waals materials with different polarization directions. WTe$_2$ is a polar metal with out-of-plane ferroelectric polarization, while SnSe ferroelectric semiconductor is polarized in-plane, so one should expect complicated polarization structure at the SnSe/WTe$_2$ interface. We study $dI/dV(V)$ curves, which demonstrate sharp symmetric drop to zero $dI/dV$ differential conductance at some threshold bias voltages $\pm V_{th}$, which are nearly symmetric in respect to the bias sign. While the gate electric field is too small to noticeably affect the carrier concentration, the positive and negative threshold positions are sensitive to the gate voltage. Also, SnSe/WTe$_2$ heterostructure shows re-entrant transition to the low-conductive $dI/dV=0$ state for abrupt change of the bias voltage even below the threshold values. This behavior can not be observed for single SnSe or WTe$_2$ flakes, so we interpret it as a result of the SnSe/WTe$_2$ interface coupling. In this case, some threshold value of the electric field at the SnSe/WTe$_2$ interface is enough to drive 90$^\circ$ change of the initial SnSe in-plane polarization in the overlap region. The polarization mismatch leads to the significant interface resistance contribution, analogously to the scattering of the charge carriers on the domain walls. Thus, we demonstrate polarization state control by electron transport through the SnSe/WTe$_2$ interface.