# Laser-induced persistent photovoltage on the surface of a ternary topological insulator at room temperature

## TL;DR

This study demonstrates that a laser-induced persistent photovoltage can be generated on the surface of a ternary topological insulator at room temperature, with potential applications in optical devices.

## Contribution

We show that optical excitation induces a long-lasting surface photovoltage in a bulk-insulating topological insulator, revealing a new mechanism for optoelectronic control.

## Key findings

- Photovoltage persists over >6 microseconds.
- Surface voltage driven solely by optical means at room temperature.
- Enhanced relaxation times of excited states in doped topological insulators.

## Abstract

Using time- and angle-resolved photoemission, we investigate the ultrafast response of excited electrons in the ternary topological insulator (Bi$_{1 x}$Sb$_{x}$)$_2$Te$_3$ to fs-infrared pulses. We demonstrate that at the critical concentration $x$=0.55, where the system becomes bulk insulating, a surface voltage can be driven at room temperature through the topological surface state solely by optical means. We further show that such a photovoltage persists over a time scale that exceeds $\sim$6 $\mu$s, i.e, much longer than the characteristic relaxation times of bulk states. We attribute the origin of the photovoltage to a laser-induced band-bending effect which emerges near the surface region on ultrafast time scales. The photovoltage is also accompanied by a remarkable increase in the relaxation times of excited states as compared to undoped topological insulators. Our findings are relevant in the context of applications of topological surface states in future optical devices.