Insulator-to-Metal Transition and Anomalously Slow Hot Carrier Cooling in a Photo-doped Mott Insulator

TL;DR

This study uses ultrafast electron microscopy to visualize the slow hot carrier cooling and insulator-to-metal transition in a photo-doped Mott insulator, revealing unique transport dynamics and phase changes.

Contribution

First direct real-space imaging of photoexcited carrier dynamics in a Mott insulator, showing long-lived hot carriers and nonlinear phase transition behavior.

Findings

Hot photocarrier transport lasts over one nanosecond.

Observation of photo-induced insulator-to-metal transition at high fluences.

Demonstration of SUEM's capability to probe strongly correlated systems.

Abstract

Photo-doped Mott insulators can exhibit novel photocarrier transport and relaxation dynamics and non-equilibrium phases. However, time-resolved real-space imaging of these processes are still lacking. Here, we use scanning ultrafast electron microscopy (SUEM) to directly visualize the spatial-temporal evolution of photoexcited species in a spin-orbit assisted Mott insulator {\alpha}-RuCl3. At low optical fluences, we observe extremely long hot photocarrier transport time over one nanosecond, almost an order of magnitude longer than any known values in conventional semiconductors. At higher optical fluences, we observe nonlinear features suggesting a photo-induced insulator-to-metal transition, which is unusual in a large-gap Mott insulator. Our results demonstrate the rich physics in a photo-doped Mott insulator that can be extracted from spatial-temporal imaging and showcase the capability of SUEM to sensitively probe photoexcitations in strongly correlated electron systems.