Floquet-Volkov spin polarization in spin-degenerate Antiferromagnets

Abstract

Periodic driving enables ultrafast control of electronic structures in solids through the formation of photon-dressed Floquet-Bloch states. However, the measured photoemission spectra are influenced not only by these states but also by their interference with Volkov-dressed outgoing photoelectrons. Here, we demonstrate that Floquet-Volkov interference can generate spin-polarized photoemission in a collinear antiferromagnetic Dirac model without spin-orbit coupling (SOC). An in-plane linearly polarized pump preserves $\mathcal{PT}$ symmetry, leaving the Floquet quasienergies spin degenerate. Under near-resonant driving, photon-dressed conduction and valence bands hybridize, producing spin-dependent relative phases that are converted into unequal spin-resolved photoemission intensities through interference between pathways reaching the same Volkov-dressed final state. We analytically identify this interference mechanism and verify it using nonequilibrium Green-function calculations under periodic driving and finite pump-probe pulses. We further demonstrate that rotating the probe polarization can suppress or reverse the spin polarization without modifying the Floquet bands. Our findings establish Floquet-Volkov interference as a route to spin-selective photoemission in driven antiferromagnets without Floquet spin splitting or SOC.