Phase separation and the phase diagram of cuprate superconductors

Abstract

We show that the main features of the cuprate superconductor phase diagram can bederived considering the disorder as a key property of these materials. Our basic point isthat the high pseudogap line is an onset of phase separation which generatescompounds made up of regions with distinct doping levels. We calculate howthis continuous temperature dependent phase separation process occurs in highcritical temperature superconductors (HTSC) using the Cahn–Hilliard approach,originally applied to study alloys. Since the level of phase separation varies fordifferent cuprates, it is possible that different systems with average doping levelpm exhibit different degrees of charge and spin segregation. Calculations on inhomogeneouscharge distributions in the form of stripes on finite clusters performed bythe Bogoliubov–de Gennes superconducting approach yield good agreementbetween the onset of local pairing amplitude and the pseudogap temperatureT*(pm). Assuming that the local order parameters generated at these clusters havetheir phase locked, we can follow how the superconducting phase develops atTc(pm) by possible percolation or Josephson coupling.