Atomic Lattice Disorder in Charge Density Wave Phases of Exfoliated Dichalcogenides (1T-TaS2)

TL;DR

This study uses atomic resolution microscopy to directly image charge density wave-related lattice distortions in exfoliated 1T-TaS2, revealing stacking transitions and domain structures that influence electronic phases.

Contribution

It provides the first direct atomic-scale imaging of PLDs and stacking transitions in exfoliated 1T-TaS2, linking lattice disorder to electronic phase control.

Findings

Observation of commensurate and nearly-commensurate PLDs at different temperatures.

Discovery of stacking transitions via bond length shifts.

Presence of NC PLDs within stacking domains and boundaries.

Abstract

Charge density waves (CDW) and their concomitant periodic lattice distortions (PLD) govern the electronic properties in many layered transition-metal dichalcogenides. In particular, 1T-TaS2 undergoes a metal-to-insulator phase transition as the PLD becomes commensurate with the crystal lattice. Here we directly image PLDs of the nearly-commensurate (NC) and commensurate (C) phases in thin exfoliated 1T-TaS2 using atomic resolution scanning transmission electron microscopy at room and cryogenic temperature. At low temperatures, we observe commensurate PLD superstructures, suggesting ordering of the CDWs both in- and out-of-plane. In addition, we discover stacking transitions in the atomic lattice that occur via one bond length shifts. Interestingly, the NC PLDs exist inside both the stacking domains and their boundaries. Transitions in stacking order are expected to create fractional shifts in the CDW between layers and may be another route to manipulate electronic phases in layered dichalcogenides.