Ultrafast spin polarization control of Dirac fermions in topological insulators

TL;DR

This paper demonstrates the ultrafast optical control of spin polarization in topological insulator surface states using femtosecond light pulses, enabling potential applications in high-speed spintronics.

Contribution

It provides the first direct observation of ultrafast spin polarization switching in topological insulators with all-optical methods.

Findings

Achieved all-optical switching of out-of-plane spin polarization

Spin polarization relaxes within approximately 1.2 picoseconds

Established feasibility of ultrafast optical control of Dirac fermions

Abstract

Three-dimensional topological insulators (TIs) are characterized by spin-polarized Dirac-cone surface states that are protected from backscattering by time-reversal symmetry. Control of the spin polarization of topological surface states (TSSs) using femtosecond light pulses opens novel perspectives for the generation and manipulation of dissipationless surface spin currents on ultrafast timescales. Using time-, spin-, and angle-resolved spectroscopy, we directly monitor for the first time the ultrafast response of the spin polarization of photoexcited TSSs to circularly-polarized femtosecond pulses of infrared light. We achieve all-optical switching of the transient out-of-plane spin polarization, which relaxes in about 1.2 ps. Our observations establish the feasibility of ultrafast optical control of spin-polarized Dirac fermions in TIs and pave the way for novel optospintronic applications at ultimate speeds.