Exceptional non-reciprocity in non-Hermitian spin dynamics

We investigate topological structure of complex energy surfaces of non-equilibrium magnetic systems. We consider spin-transfer torque-driven single-spin model described by a non-Hermitian Hamiltonian. The spectrum of the Hamiltonian admits branch point singularities that appear as chiral exceptional points where both eigenvalues and eigenstates coalesce. The emergence of exceptional spectral points provides access to a wealth of topological effects unique to non-Hermitian spin systems, e.g. non-reciprocal spin dynamics. An implementation of an asymmetric spin-filter device based on this effect is proposed.