Coherent control over three-dimensional spin polarization for the spin-orbit coupled surface state of Bi$_2$Se$_3$

TL;DR

This study demonstrates coherent control of three-dimensional spin polarization in the surface state of Bi$_2$Se$_3$ using laser photoemission, revealing quantum spin superpositions and rotations manipulable by laser polarization.

Contribution

It introduces a laser photoemission method to visualize and control coherent spin superpositions and rotations in topological insulator surface states.

Findings

Linearly polarized laser excites spin-up and spin-down states simultaneously.

Quantum spin superpositions are coherently manipulated by laser polarization.

Full spin rotation phase is observed, revealing quantum spin dynamics.

Abstract

Interference of spin-up and spin-down eigenstates depicts spin rotation of electrons, which is a fundamental concept of quantum mechanics and accepts technological challenges for the electrical spin manipulation. Here, we visualize this coherent spin physics through laser spin- and angle-resolved photoemission spectroscopy on a spin-orbital entangled surface-state of a topological insulator. It is unambiguously revealed that the linearly polarized laser can simultaneously excite spin-up and spin-down states and these quantum spin-basis are coherently superposed in photoelectron states. The superposition and the resulting spin rotation is arbitrary manipulated by the direction of the laser field. Moreover, the full observation of the spin rotation displays the phase of the quantum states. This presents a new facet of laser-photoemission technique for investigation of quantum spin physics opening new possibilities in the field of quantum spintronic applications.