Photoinduced two-step insulator-metal transition in Ti4O7 by ultrafast time-resolved optical reflectivity

TL;DR

This study investigates ultrafast optical reflectivity in Ti4O7, revealing a two-step photoinduced insulator-metal transition with potential applications in photoelectric and thermoelectric devices.

Contribution

It demonstrates that ultrafast photoexcitation can control the two-step insulator-metal transition in Ti4O7 by lowering transition temperatures.

Findings

Identification of two distinct phase transitions in Ti4O7

Photoexcitation lowers transition temperatures Tc1 and Tc2

Provides a phase diagram for photoinduced insulator-metal transition

Abstract

We report on systematic investigation of hot carrier dynamics in Ti4O7 by ultrafast time-resolved optical reflectivity. We find the transient indication for its two-step insulator-metal (I-M) transition, in which two phase transitions occur from long-range order bipolaron low-temperature insulating (LI) phase to disordered bipolaron high-temperature insulating (HI) phase at Tc1 and to free carrier metallic (M) phase at Tc2. Our results reveal that photoexcitation can effectively lower down both Tc1 and Tc2 with pump fluence increasing, allowing a light-control of I-M transition. We address a phase diagram that provides a framework for the photoinduced I-M transition and helps the potential use of Ti4O7 for photoelectric and thermoelectric devices.