Non-Hermitian band topology from momentum-dependent relaxation in two-dimensional metals with spiral magnetism

We study the emergence of non-Hermitian band topology in a two-dimensional metal with planar spiral magnetism due to a momentum-dependent relaxation rate. A sufficiently strong momentum dependence of the relaxation rate leads to exceptional points in the Brillouin zone, where the Hamiltonian is nondiagonalizable. The exceptional points appear in pairs with opposite topological charges and are connected by arc-shaped branch cuts. We show that exceptional points inside hole and electron pockets, which are generally present in a spiral magnetic state with a small magnetic gap, can cause a drastic change of the Fermi surface topology by merging those pockets at isolated points in the Brillouin zone. We derive simple rules for the evolution of the eigenstates under semiclassical motion through these crossing points, which yield geometric phases depending only on the Fermi surface topology. The spectral function observed in photoemission exhibits Fermi arcs. Its momentum dependence is smooth-despite of the nonanalyticities in the complex quasiparticle band structure.

Automated summary

In this study, the emergence of non-Hermitian band topology in a two-dimensional metal with planar spiral magnetism is investigated. The research reveals that a momentum-dependent relaxation rate can lead to exceptional points in the Brillouin zone, resulting in pairs of opposite topological charges connected by arc-shaped branch cuts. Additionally, these exceptional points can cause a drastic change in the Fermi surface topology by merging electron and hole pockets at isolated points in the Brillouin zone.