Distinct surface and bulk charge density waves in ultrathin 1T-TaS2

Abstract

We employ low-frequency Raman spectroscopy to study the nearly commensurate (NC) to commensurate (C) charge density wave (CDW) transition in 1T-TaS2 ultrathin flakes protected from oxidation. We identify new modes originating from C phase CDW phonons that are distinct from those seen in bulk 1T-TaS2. We attribute these to CDW modes from the surface layers. By monitoring individual modes with temperature, we find that surfaces undergo a separate, low-hysteresis NC-C phase transition that is decoupled from the transition in the bulk layers. This indicates the activation of a secondary phase nucleation process in the limit of weak interlayer interaction, which can be understood from energy considerations.

References in corpus (2)

• Gate-tunable Phase Transitions in 1T-TaS${}_2$
• Zone-center phonons of bulk, few-layer, and monolayer 1T-TaS${}_2$: Detection of the commensurate charge density wave phase through Raman scattering

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