Effect of paramagnon drag on thermoelectric transport properties: Linear response theory

Paramagnetic materials exhibit a unique thermoelectric effect near the ferromagnetic transition point due to spin fluctuations. This phenomenon is referred to as paramagnon drag. In this study, we calculate the contribution of this paramagnon drag to the Seebeck coefficient microscopically based on the linear response theory. Consequently, we obtain a general formula for the contribution to the Seebeck coefficient due to the paramagnon drag and then clarify the conditions in which the Seebeck coefficient is enhanced near the ferromagnetic transition point for a single-band and isotropic system. Moreover, we calculate the Seebeck coefficients for a mixture of free-electron-like and flat bands.