Finite temperature second harmonic generation in Kitaev magnets

Abstract: We study electric field induced second harmonic generation (2HG) in the Kitaev model. This frustrated magnet hosts a quantum spin-liquid, featuring fractionalization in terms of mobile Majorana fermion and static $\mathbb{Z}_{2}$ flux-vison elementary excitations. We show that finite temperature 2HG allows to probe characteristic features of both fractional quasiparticle types. In the homogeneous flux state at low-temperatures, the 2HG susceptibility displays an oscillatory spectrum, which is set by only the fermionic excitations and is subject to temperature induced Fermi-blocking, generic to all higher harmonic generation (HHG). In the intermediate to high temperature range, intrinsic randomness, which emerges from thermally excited visons leads to drastic changes of the 2HG susceptibility, resulting from resonance decoupling over a wide range of energies. At the flux proliferation crossover, we suggest an interpolation between these two temperature regimes. Our results satisfy previously established symmetries for electric field induced 2HG in Kitaev magnets.