Sublattice asymmetry and spin-orbit interaction induced out-of-plane spin polarization of photoelectrons

TL;DR

This paper theoretically investigates how sublattice asymmetry and spin-orbit coupling in graphene induce out-of-plane spin polarization of photoelectrons, enabling detection of small band gaps via spin-resolved photoemission spectroscopy.

Contribution

It reveals that sublattice asymmetry combined with spin-orbit interaction causes out-of-plane spin polarization, providing a new method to detect small band gaps in graphene.

Findings

Out-of-plane spin polarization arises near the Dirac point due to sublattice asymmetry and spin-orbit coupling.

Spin-resolved photoemission can detect small band gaps not visible in standard ARPES.

Analytical and numerical models describe energy and linewidth dependence of spin polarization.

Abstract

We study theoretically the effect of spin-orbit coupling and sublattice asymmetry in graphene on the spin polarization of photoelectrons. We show that sublattice asymmetry in graphene not only opens a gap in the band structure but in case of finite spin-orbit interaction it also gives rise to an out-of-plane spin polarization of electrons close to the Dirac point of the Brillouin zone. This can be detected by measuring the spin polarization of photoelectrons and therefore spin resolved photoemission spectroscopy can reveal the presence of a band gap even if it is too small to be observed directly by angle resolved photoemission spectroscopy because of the finite resolution of measurements or because the sample is $p$-doped. We present analytical and numerical calculations on the energy and linewidth dependence of photoelectron intensity distribution and spin polarization.