Peculiar transport mechanisms of charge carriers in the normal state of underdoped cuprate superconductors

We study the peculiar charge transport properties of high-Tc cuprate superconductors by considering distinctive transport mechanisms of the three types of charge carriers (large polarons, excited components of polaronic (bosonic) Cooper pairs, and bosonic Cooper pairs themselves) in the normal state of underdoped and optimally doped cuprates. For a specific cuprate considered, we calculate the conductivity of the aforementioned charge carriers by means of their scattering on acoustic and optical phonons above the superconducting transition temperature Tc. As a result, clearly distinguishable ranges of the temperature dependence of the in-plane resistivity ρab(T) both above and below the pseudogap formation temperature T∗(>Tc) demonstrate completely different behavior compared to that which is expected for conventional Fermi-liquid metals, thus providing strong support for novel metallic states. Our theoretical results, compared with the experimental data, allow to consistently explain various anomalous behaviors of the ρab(T) observed in La-, Y-, and Bi-based cuprate superconductors above Tc. We conclude that in underdoped and optimally doped cuprates, above T∗, the scattering of polaronic carriers by acoustic and optical phonons is responsible for the linear tendency of the ρab(T), while its corresponding downward and upward deviations from the linearity below T∗ are caused by the dominating conductivity of bosonic Cooper pairs and by the effect of the BCS-like pseudogap on the conductivity of the excited (dissociated) polaronic components in the normal state.