Ultrafast Energy- and Momentum-resolved Surface Dirac Photocurrents in the Topological Insulator Sb$_2$Te$_3$

TL;DR

This study maps and controls ultrafast surface Dirac photocurrents in Sb$_2$Te$_3$ using advanced spectroscopy, revealing dynamics and enabling coherent optical manipulation of topological surface states.

Contribution

It demonstrates direct optical control of surface Dirac electrons and visualizes their ultrafast dynamics in a topological insulator using time- and angle-resolved photoemission.

Findings

Linear and circular photogalvanic effects enable control of surface currents.

Ultrafast intraband relaxation and momentum scattering are separately observed.

Surface current dynamics are visualized in real-time.

Abstract

We present energy-momentum mapping of surface Dirac photocurrent in the topological insulator Sb$_2$Te$_3$ by means of time- and angle-resolved two-photon photoemission spectroscopy combined with polarization-variable mid-infrared pulse laser. It is demonstrated that the direct optical transition from the occupied to the unoccupied part of the surface Dirac-cone permits the linear and circular photogalvanic effect which thereby enables us to coherently control the surface electric-current by laser polarization. Moreover, the surface current mapping directly visualizes ultrafast current dynamics in the Dirac cone in the time domain. We unravel the ultrafast intraband relaxation dynamics of the inelastic scattering and momentum scattering separately. Our observations pave the pathway for coherent optical control over surface Dirac electrons in topological insulators.