Electrical Conductivity in the Hubbard Model Including Electron‐Phonon Interaction

Using the Hubbard model including weak electron‐phonon coupling the electrical conductivity σ is calculated for U ≫ t (U intra‐atomic Coulomb energy, —t nearest‐neighbour hopping integral) and low frequencies. Especially the dc conductivity is investigated for the half‐filled band and T ≫ TD (TD Debye temperature). It is compared with the dc conductivity in the phononless Hubbard model calculated in the approximation lim (σ/t2). The inclusion of phonons results in t → 0 a finite transport relaxation time the temperature dependence of which leads to a shift of the conductivity maximum temperature to a lower value, the sharpening of the maximum, and to the decrease of the conductivity for high temperatures according to T−2.