Ultrafast Optical Excitation of a Persistent Surface-State Population in the Topological Insulator Bi2Se3

TL;DR

This study uses femtosecond spectroscopy to observe long-lived nonequilibrium populations in the surface states of Bi2Se3, revealing potential for transient spin-polarized current applications.

Contribution

It demonstrates the ultrafast optical excitation of a persistent surface-state population in Bi2Se3, a novel observation of long-lived nonequilibrium states in topological insulators.

Findings

Long-lived (>10 ps) surface state population observed after optical excitation.

Population at the bulk conduction band edge feeds the surface state.

Potential for driving transient spin-polarized currents.

Abstract

Using femtosecond time- and angle- resolved photoemission spectroscopy, we investigated the nonequilibrium dynamics of the topological insulator Bi2Se3. We studied p-type Bi2Se3, in which the metallic Dirac surface state and bulk conduction bands are unoccupied. Optical excitation leads to a meta-stable population at the bulk conduction band edge, which feeds a nonequilibrium population of the surface state persisting for >10ps. This unusually long-lived population of a metallic Dirac surface state with spin texture may present a channel in which to drive transient spin-polarized currents.