Cavity-modified Zeeman effect via spin-polariton formation

We study the electronic spin Zeeman effect for an effective spin-1/2-system subject to both strong coupling to a low-frequency optical cavity and an external static magnetic field. In particular, we address the interplay between the cavity magnetic field component in a cavity Zeeman interaction and the canonical spin Zeeman interaction from the perspective of an effective spin-polariton Hamiltonian. The latter is derived from the minimal coupling Pauli-Fierz Hamiltonian beyond the common dipole approximation via first-order quasi-degenerate perturbation theory. We find the spin Zeeman effect to be modified in the presence of the cavity field due to the formation of spin-polariton states, which result from an intricate interplay of cavity and external magnetic fields in our model. Spin-polariton signatures are discussed in the context of electron paramagnetic resonance spectroscopy along with cavity-induced modifications of the electronic g-factor.