Infrared nanoimaging of the metal-insulator transition in the charge-density-wave van der Waals material 1T−TaS2

Abstract

Using scanning near-field optical microscopy at cryogenic temperatures, we explored the first-order metal-insulator transition of exfoliated 1T-TaS2 microcrystals on a SiO2/Si substrate. We clearly observed spatially-separated metallic and insulating states during the transition between commensurate and nearly-commensurate charge density wave phases. The capability to probe electrodynamics on nanometer length scales revealed temperature-dependent electronic properties of the insulating and metallic regions near the transition temperature. At fixed temperature, a remarkably broad spatial boundary between insulating and metallic regions was observed, across which the nano-optical signal smoothly evolved over a length scale of several hundred nanometers. In order to understand these observations, we performed Ginzburg-Landau calculations to determine the charge density wave structure of the domain boundary, which revealed the existence of an intermediate electronic phase with unique properties distinct from the bulk thermodynamic phases.

Photocurrent Imaging of Multi-Memristive Charge Density Wave Switching in Two-Dimensional 1T-TaS2

“…S5). This is also consistent with previous nanoscale infrared imaging on a 1T-TaS2 flake with moderate thickness 23 . Taken together, these measurements demonstrate the utility of our photocurrent scheme in deciphering spatial differences in the NC-C transition of 1T-TaS2 on the micron scale that is relevant for electronic devices.…”

Modern Scattering‐Type Scanning Near‐Field Optical Microscopy for Advanced Material Research

“…In CW visible/IR s‐SNOM research, a wide range of canonical systems have been intensely investigated. The major categories in condensed matter systems include, but are not limited to, mesoscopic phase inhomogeneity in strongly correlated quantum materials (SCQM), polaritonic wave propagation in plasmonic or dielectric samples, especially low‐dimensional materials (graphene, boron nitride, transition metal dichalcogenides, etc. ), and subwavelength electrodynamic responses from artificial nanostructures …”

Observation and manipulation of a phase separated state in a charge density wave material

“…Only recently have attempts been made to specifically study the spatial characteristics of the phases present in flakes within the NC-C hysteresis region, but these experiments have been limited to characterizing the phases at the micron length scale. 14,18,19 In this work, the nanoscopic nature of the CDW states in the hysteresis region of the NC-C phase transition of ultrathin 1T-TaS 2 is elucidated. We image exfoliated flakes using scanning tunneling microscopy (STM) and observe the existence of an inhomogeneous electronic state.…”