In-plane resistivity and an explanation for the characteristicT*in high-Tccuprates

Abstract

We offer an explanation for the observed crossover temperature ${T}^{*}$ in in-plane resistivity ${\ensuremath{\rho}}_{\mathrm{ab}}$ of biplanar high-${T}_{c}$ cuprates. The key to our picture is the existence of nondegenerate and degenerate carriers possessing different quasiparticle relaxation rates. In the underdoped regime the change of slope $d{\ensuremath{\rho}}_{\mathrm{ab}}/dT$ at ${T}^{*}$ results from the thermal activation of nondegenerate carriers. In the overdoped regime, the nondegenerate carriers tend to become degenerate and a second small Fermi energy emerges, resulting in a change to ${T}^{2}$ behavior in ${\ensuremath{\rho}}_{\mathrm{ab}}$ at low T. We compare our results with data on several compounds. We also find an approximate scaling in conductivity.