A Gapped Phase in Semimetallic T$_{d}$-WTe$_{2}$ Induced by Lithium Intercalation

TL;DR

This paper reports the discovery of a new charge density wave phase in T$_{d}$-WTe$_{2}$ induced by lithium intercalation, characterized by increased resistivity, reduced carrier density, and structural distortions, expanding the understanding of phase control in 2D materials.

Contribution

It provides the first experimental evidence of a CDW phase in T$_{d}$-WTe$_{2}$ and demonstrates lithium intercalation as an effective method to induce and study new electronic phases.

Findings

Lithium intercalation induces a gapped CDW phase in WTe$_{2}$.

The new phase exhibits a bandgap of approximately 0.14 eV.

Structural analysis shows large lattice distortions near 6%.

Abstract

The Weyl semimetal WTe$_{2}$ has shown several correlated electronic behaviors, such as the quantum spin Hall effect, superconductivity, ferroelectricity, and a possible exciton insulator state, all of which can be tuned by various physical and chemical approaches. Here, we discover a new electronic phase in WTe$_{2}$ induced by lithium intercalation. The new phase exhibits an increasing resistivity with decreasing temperature and its carrier density is almost two orders of magnitude lower than the carrier density of the semi-metallic T$_{d}$ phase, probed by in situ Hall measurements as a function of lithium intercalation. Our theoretical calculations predict the new lithiated phase to be a charge density wave (CDW) phase with a bandgap of ~ 0.14 eV, in good agreement with the in situ transport data. The new phase is structurally distinct from the initial T$_{d}$ phase, characterized by polarization angle-dependent Raman spectroscopy, and large lattice distortions close to 6 % are predicted in the new phase. Thus, we report the first experimental evidence of CDW in T$_{d}$-WTe$_{2}$, projecting WTe$_{2}$ as a new playground for studying the interplay between CDW and superconductivity. Our finding of a new gapped phase in a two-dimensional (2D) semi-metal also demonstrates electrochemical intercalation as a powerful tuning knob for modulating electron density and phase stability in 2D materials.