Polaronic conductivity in the photoinduced phase of 1T-TaS2

TL;DR

This study investigates the transient optical conductivity of photoexcited 1T-TaS2, revealing polaronic transport characteristics in a unique photoinduced metallic state where the Mott gap is melted but lattice symmetry remains unchanged.

Contribution

It demonstrates that the photoinduced metallic state in 1T-TaS2 exhibits polaronic transport, distinct from thermally-driven transitions, by combining optical measurements with analysis of lattice and electronic properties.

Findings

Transient metallic state shows suppressed low-frequency conductivity.

Fano phonon lineshapes indicate polaronic behavior.

Mid-infrared absorption band supports polaronic transport hypothesis.

Abstract

The transient optical conductivity of photoexcited 1T-TaS2 is determined over a three-order-of-magnitude frequency range. Prompt collapse and recovery of the Mott gap is observed. However, we find important differences between this transient metallic state and that seen across the thermally-driven insulator-metal transition. Suppressed low-frequency conductivity, Fano phonon lineshapes, and a mid-infrared absorption band point to polaronic transport. This is explained by noting that the photo-induced metallic state of 1T-TaS2 is one in which the Mott gap is melted but the lattice retains its low-temperature symmetry, a regime only accessible by photo-doping.