Widespread spin polarization effects in photoemission from topological insulators

TL;DR

This study uses advanced spin-resolved photoemission spectroscopy to reveal complex spin polarization effects in topological insulators, highlighting the importance of careful interpretation of experimental data due to unexpected spin phenomena.

Contribution

It uncovers additional spin polarization effects in topological insulators that are distinct from topological surface states, emphasizing the complexity of spin-resolved measurements.

Findings

Observation of helical spin structure in Bi2Se3 surface states

Detection of unexpected spin polarization effects from spin-orbit interaction

Demonstration of deviations between photoelectron and quasiparticle spins

Abstract

High resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES) was performed on the three-dimensional topological insulator Bi$_2$Se$_3$ using a recently developed high-efficiency spectrometer. The topological surface state's helical spin structure is observed, in agreement with theoretical prediction. Spin textures of both chiralities, at energies above and below the Dirac point, are observed, and the spin structure is found to persist at room temperature. The measurements reveal additional unexpected spin polarization effects, which also originate from the spin-orbit interaction, but are well differentiated from topological physics by contrasting momentum and photon energy and polarization dependencies. These observations demonstrate significant deviations of photoelectron and quasiparticle spin polarizations. Our findings illustrate the inherent complexity of spin-resolved ARPES and demonstrate key considerations for interpreting experimental results.