Charge density waves and degenerate modes in exfoliated monolayer 2H-TaS2.

Duan Zhang,Byong Sun Chun,Yecun Wu,Jiung Cho,Ming-Chien Hsu,Yu-Hsin Su,Ching-Ray Chang,Han-Chun Wu,Cormac Ó Coileáin,Yao Guo,Miri Choi

doi:10.1107/s2052252520011021

Abstract

Charge density waves spontaneously breaking lattice symmetry through periodic lattice distortion, and electron-electron and electron-phonon inter-actions, can lead to a new type of electronic band structure. Bulk 2H-TaS2 is an archetypal transition metal dichalcogenide supporting charge density waves with a phase transition at 75 K. Here, it is shown that charge density waves can exist in exfoliated monolayer 2H-TaS2 and the transition temperature can reach 140 K, which is much higher than that in the bulk. The degenerate breathing and wiggle modes of 2H-TaS2 originating from the periodic lattice distortion are probed by optical methods. The results open an avenue to investigating charge density wave phases in two-dimensional transition metal dichalcogenides and will be helpful for understanding and designing devices based on charge density waves.

Highlights

Structural charge density waves (CDWs), transitions from a normal to a distorted phase, have been extensively studied for many decades (Gruner, 1988)
CDW transitions are known to occur in a wide variety of materials, a prominent example being layered transition metal dichalcogenides (TMDs), which have received much attention due to their novel optical and electronic properties
In this work, based on density functional simulations, we demonstrate that CDWs can exist in exfoliated monolayer 2HTaS2 and the transition temperature is much higher than that in the bulk

Summary

Introduction

Structural charge density waves (CDWs), transitions from a normal to a distorted phase, have been extensively studied for many decades (Gruner, 1988). It has been suggested that it is possible to tune the CDW transition temperature of thin TMDs through dimensionality (Xi et al, 2015), electrostatic gating (Yu et al, 2015) or strain engineering (Gao et al, 2018). This would enable the quantum phase transitions to be controlled in a manner that is compatible with current semiconductor technology

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