Endotaxial Stabilization of 2D Charge Density Waves with Long-range Order

TL;DR

This study demonstrates the stabilization of long-range ordered 2D charge density waves in monolayer 1T-TaS2 through endotaxial synthesis, revealing new phase behaviors and the melting process involving topological defects.

Contribution

It introduces endotaxial synthesis as a method to stabilize ordered 2D charge density waves, enabling detailed study of their phase transitions and topological defect formation.

Findings

Enhanced amplitude and resistivity of 2D CDWs

Observation of a reversible hexatic melting process

Identification of new regimes in the CDW phase diagram

Abstract

Charge density waves are emergent quantum states that spontaneously reduce crystal symmetry, drive metal-insulator transitions, and precede superconductivity. In low-dimensions, distinct quantum states arise, however, thermal fluctuations and external disorder destroy long-range order. Here we stabilize ordered two-dimensional (2D) charge density waves through endotaxial synthesis of confined monolayers of 1T-TaS$_2$. Specifically, an ordered incommensurate charge density wave (oIC-CDW) is realized in 2D with dramatically enhanced amplitude and resistivity. By enhancing CDW order, the hexatic nature of charge density waves becomes observable. Upon heating via in-situ TEM, the CDW continuously melts in a reversible hexatic process wherein topological defects form in the charge density wave. From these results, new regimes of the CDW phase diagram for 1T-TaS$_2$ are derived and consistent with the predicted emergence of vestigial quantum order.