Thermoelectric power of metallic Rb_3 C_60: phonon-drag and carrier diffusion contributions

Thermoelectric power (5) of Rb_3 C_60 fullerides in the metallic phase is theoretically estimated. We first develop a Hamiltonian model that incorporates the scattering rates within the relaxation time approximation to estimate the phonon-drag thermoelectric power (S^drag_ph) incorporating the scattering of phonons with defects, electrons as carriers, grain boundaries, and phonon-phonon interactions. As a next step, Mott expression within parabolic band approximation is used to analyze the electron diffusive thermoelectric power (S^diff_C) using Fermi energy as electron parameter, and S^diff_C shows a linear temperature dependence. The S^drag_ph is nonzero in both normal and superconducting states. Its behavior is determined by competition among the several operating scattering rates for heat carriers and a balance between diffusive carrier and phonon-drag contributions. Acoustic phonons are effectively scattered by various scatterers for the thermoelectric power. S infers a change in slope above transition temperature and becomes almost linear above 70 K.