Finite Temperature Crossover in thed-pModel

Abstract

We investigate finite temperature properties of the U d -infinite d-p model in the auxiliary boson representation within the leading order approximation in the 1/ N -expansion. We obtain a unified description of the system valid over the whole temperature range divided by the two characteristic energies, the binding eppnergy of the resonance state of the auxiliary boson, ω 0 , and the coherence temperature, T 0 , of O (ω 0 /10). At T ≪ T 0 , a new coherent band (in-gap band) appears inside the charge-transfer gap upon carrier doping and behaves as Fermi liquid with large Fermi surface determined by the Luttinger sum rule. The band width is an increasing function of carrier doping rate and of O (ω 0 ). At T >ω 0 , the chemical potential is below the in-gap band and the doped holes are mostly on the O-2p band forming small Fermi surface, while the Cu-3 d holes behave like spin-\(\frac{1}{2}\) localized moments. At \(T_{0}\preceq T\preceq \omega _{0}\), crossover phenomena between the two limiting cases are ...