Mechanically tunable spontaneous vertical charge redistribution in few-layer WTe2

TL;DR

This study demonstrates that layer stacking in few-layer WTe2 creates surface dipoles that can be mechanically tuned, affecting charge distribution, magnetoresistance, and spin textures, with implications for electronic and spintronic applications.

Contribution

The paper reveals that unique layer stacking in WTe2 generates tunable surface dipoles, influencing charge and spin properties, and explains ferroelectric-like behavior in atomically thin films.

Findings

Surface dipoles vary with layer stacking in WTe2.

Interlayer shear displacement can switch surface dipoles.

Exfoliation flips out-of-plane spin textures.

Abstract

Broken symmetry is the essence of exotic properties in condensed matters. Tungsten ditelluride, WTe$_2$, exceptionally takes a non-centrosymmetric crystal structure in the family of transition metal dichalcogenides, and exhibits novel properties$^{1-4}$, such as the nonsaturating magnetoresistance$^1$ and ferroelectric-like behavior$^4$. Herein, using the first-principles calculation, we show that unique layer stacking in WTe$_2$ generates surface dipoles with different strengths on the top and bottom surfaces in few-layer WTe$_2$. This leads to a layer-dependence for electron/hole carrier ratio and the carrier compensation responsible for the unusual magnetoresistance. The surface dipoles are tunable and switchable using the interlayer shear displacement. This could explain the ferroelectric-like behavior recently observed in atomically thin WTe$_2$ films$^4$. In addition, we reveal that exfoliation of the surface layer flips the out-of-plane spin textures. The presented results will aid in the deeper understanding, manipulation, and further exploration of the physical properties of WTe$_2$ and related atom-layered materials, for applications in electronics and spintronic devices.