Photoinduced two-step insulator-metal transition in Ti_4O_7 via ultrafast time-resolved optical reflectivity

摘要

We report on the 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, i.e., from the long-range ordered bipolaron low-temperature insulating phase to the disordered bipolaron high-temperature insulating phase at T-c1 and to the free-carrier metallic phase at T-c2. Our results reveal that photoexcitation can effectively reduce both T-c1 and T-c2 by increasing the pump fluence, allowing the light-control of the 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. (C) 2018 The Japan Society of Applied Physics