Phenomenological analysis of the low temperature

Abstract

The low-temperature phase diagram of a high-temperature cuprate superconductor consists of the superconducting, pseudogap and normal phases is analyzed in yttrium barium copper oxide systems by a phenomenological scheme using the shallow valence band electronic structure. The superconducting and pseudogap phases, which involve condensates, are assumed to be equilibrium systems of the condensate and normal subphases. The condition for phase transitions is given by equality of the total electronic energy gains. Using the mean strength of the pairing energy reproduces the experimental data well and the strength of the pairing energy decreases with increasing charge carrier concentration from the under-doped regime to the over-doped regime. We propose that this result can be explained by the screening effect.