Spin Seebeck effect in nonmagnetic excitonic insulators

We propose a mechanism of the spin Seebeck effect attributed to excitonic condensation in nonmagnetic insulator. analyze half-filled two-orbital Hubbard model with crystalline field splitting strong coupling limit. In this model, competition between and electron correlations brings about an insulating state, where two orbitals are spontaneously hybridized. Using generalized spin-wave theory Boltzmann transport equation, we find that current generated by thermal gradient is observed state without magnetic fields. The originates from spin-split collective excitation modes although ground does not exhibit any orderings. This peculiar phenomenon inherent whose order parameter time-reversal odd yields for modes. also strongly enhanced its direction inverted vicinity phase transition another magnetically ordered phase. suggest present possibly perovskite cobaltites $\mathrm{Gd}\mathrm{Fe}{\mathrm{O}}_{3}$-type lattice distortion.