Gigantic surface life-time of an intrinsic topological insulator revealed via time-resolved (pump-probe) ARPES

TL;DR

This study reveals an exceptionally long surface state lifetime exceeding 4 microseconds in the topological insulator Bi2Te2Se, contrasting with shorter lifetimes in other TIs, and uncovers a significant surface photo-voltage effect.

Contribution

It demonstrates an unprecedented surface state lifetime in Bi2Te2Se and introduces the observation of a large surface photo-voltage in topological insulators.

Findings

Surface states in Bi2Te2Se have a lifetime over 4 microseconds.

A surface photo-voltage shift of up to 100 mV is observed.

Contrast with shorter lifetimes in other topological insulators like Bi2Se3.

Abstract

The interaction between light and novel two-dimensional electronic states holds promise to realize new fundamental physics and optical devices. Here, we use pump-probe photoemission spectroscopy to study the optically-excited Dirac surface states in the bulk-insulating topological insulator Bi2Te2Se, and reveal optical properties that are in sharp contrast to those of bulk-metallic topological insulators. We observe a gigantic optical life-time exceeding 4 micro-sec for the surface states in Bi2Te2Se, whereas the life-time in most topological insulators such as Bi2Se3 has been limited to a few picoseconds. Moreover, we discover a surface photo-voltage in topological materials, a shift of the chemical potential of the Dirac surface states, as large as 100 mV. Our results demonstrate a rare platform to study charge excitation and relaxation in energy and momentum space in a two dimensional quantum system.