Spin-orbital magnetic response of relativistic fermions with band hybridization

TL;DR

This paper investigates how band hybridization affects the spin-orbital susceptibility of relativistic fermions, revealing modifications in spin polarization responses relevant for condensed matter and quark matter systems.

Contribution

It introduces the concept of spin-orbital crossed susceptibility and analyzes its modification due to band hybridization in relativistic fermions.

Findings

Hybridization modifies the spin-orbital susceptibility at the Fermi energy.

Enhanced effects occur under dynamical magnetic fields violating thermal equilibrium.

Potential experimental realizations include Dirac electrons in solids and quark matter in heavy-ion collisions.

Abstract

Spins of relativistic fermions are related to their orbital degrees of freedom. In order to quantify the effect of hybridization between relativistic and nonrelativistic degrees of freedom on spin-orbit coupling, we focus on the spin-orbital (SO) crossed susceptibility arising from spin-orbit coupling. The SO crossed susceptibility is defined as the response function of their spin polarization to the "orbital" magnetic field, namely the effect of magnetic field on the orbital motion of particles as the vector potential. Once relativistic and nonrelativistic fermions are hybridized, their SO crossed susceptibility gets modified at the Fermi energy around the band hybridization point, leading to spin polarization of nonrelativistic fermions as well. These effects are enhanced under a dynamical magnetic field that violates thermal equilibrium, arising from the interband process permitted by the band hybridization. Its experimental realization is discussed for Dirac electrons in solids with slight breaking of crystalline symmetry or doping, and also for quark matter including dilute heavy quarks strongly hybridized with light quarks, arising in a relativistic heavy-ion collision process.