Orbital-spin Locking and its Optical Signatures in Altermagnets

TL;DR

This paper introduces a microscopic model revealing how orbitals and spins couple in altermagnets, leading to unique optical signatures that enable spin-selective excitation and potential new device applications.

Contribution

It uncovers a microscopic coupling mechanism in altermagnets that links orbitals to spins and predicts optical signatures for experimental detection.

Findings

Momentum-dependent, spin-selective optical absorption in altermagnets

Controlled optical excitation of spins depending on light polarization

Proposed magneto-optical signatures for experimental validation

Abstract

Altermagnets, magnetic materials with zero magnetization and spin-split band structure, have gained tremendous attention recently for their rich physics and potential applications. Here, we report on a microscopic tight-binding model that unveils a unique coupling between orbitals and spins in $d$-wave altermagnets which gives rise to momentum-dependent and spin-selective optical absorption. This coupling promotes the controlled optical excitation of up or down spins depending on the polarization direction of linearly polarized light. Such an effect originates from the coupling of orbitals to the sublattice degree of freedom through the crystal field, which is then coupled to spins through the antiferromagnetic interaction. Our crystal field analysis, which is general to any type of altermagnet, helps understand the onset of altermagnetism from a microscopic point of view, and we use our results to propose clear magneto-optical signatures of our predictions. Our findings shine light on the interplay between orbitals and spins in altermagnets, thus paving the way towards novel orbitronic and opto-spintronic devices.