Direct observation of the layer-number-dependent electronic structure in few-layer WTe2

TL;DR

This study uses laser-based angle-resolved photoelectron spectroscopy to observe how the electronic structure of multilayer WTe2 varies with layer number, revealing an insulator-semimetal transition and spin-splitting effects.

Contribution

It provides the first direct observation of layer-dependent electronic band dispersions in multilayer WTe2, highlighting the impact of stacking on electronic properties.

Findings

Insulator-semimetal transition between 2 and 3 layers.

30-70 meV spin-splitting of valence bands in even layers.

Demonstration of large energy-scale band and spin manipulation.

Abstract

When a crystal becomes thinner and thinner to the atomic level, peculiar phenomena discretely depending on its layer-numbers (n) start to appear. The symmetry and wave functions strongly reflect the layer-numbers and stacking order, which brings us a potential of realizing new properties and functions that are unexpected in either bulk or simple monolayer. Multilayer WTe2 is one such example exhibiting unique ferroelectricity and non-linear transport properties related to the antiphase stacking and Berry-curvature dipole. Here we investigate the electronic band dispersions of multilayer WTe2 (2-5 layers), by performing laser-based micro-focused angle-resolved photoelectron spectroscopy on exfoliated-flakes that are strictly sorted by n and encapsulated by graphene. We clearly observed the insulator-semimetal transition occurring between 2- and 3-layers, as well as the 30-70 meV spin-splitting of valence bands manifesting in even n as a signature of stronger structural asymmetry. Our result fully demonstrates the possibility of the large energy-scale band and spin manipulation through the finite n stacking procedure.