Direct Observation of One-Dimensional Peierls-Type Charge Density Wave in Twin Boundaries of Monolayer MoTe$_2$

TL;DR

This study provides atomic-scale evidence of a Peierls-type charge density wave in one-dimensional twin boundaries of monolayer MoTe2, revealing new insights into electron behavior in confined 1D systems.

Contribution

First direct atomic-scale observation of a Peierls-type CDW in monolayer MoTe2 twin boundaries using STM/STS and DFT calculations.

Findings

Atomic-scale charge distribution within MTB observed.

Presence of a Peierls-type charge density wave confirmed.

Quantized energy levels associated with the CDW discovered.

Abstract

One-dimensional (1D) metallic mirror-twin boundaries (MTBs) in monolayer transition metal dichalcogenides (TMDCs) exhibit a periodic charge modulation and provide an ideal platform for exploring collective electron behavior in the confined system. The underlying mechanism of the charge modulation and how the electrons travel in 1D structures remain controversial. Here, for the first time, we observed atomic-scale structures of the charge distribution within one period in MTB of monolayer MoTe2 by using scanning tunneling microscopy/spectroscopy (STM/STS). The coexisting apparent periodic lattice distortions and U-shaped energy gap clearly demonstrate a Peierls-type charge density wave (CDW). Equidistant quantized energy levels with varied periodicity are further discovered outside the CDW gap along the metallic MTB. Density functional theory (DFT) calculations are in good agreement with the gapped electronic structures and reveal they originate mainly from Mo 4d orbital. Our work presents hallmark evidence of the 1D Peierls-type CDW on the metallic MTBs and offers opportunities to study the underlying physics of 1D charge modulation.