Spin-polarised quasiparticles in the high temperature superconductivity

The structure of spin polarised quasiparticles resonsible for the metallic phase formation has been studied in cuprate high temperature superconductors. Starting point of the model is the strong coupling of a doped hole in the CuO2 plane to Cu spin longitudinal fluctuations. It is shown that the magnetic energy used for local spin fluctuation can be overcompensated by the gained kinetic delocalisation energy. A spatially limited state is formed in which the doped hole is localised in a domain of parallel Cu spin polarisation. Using various effective field approximations it is found that such clusters consists of 5 parallel oriented Cu spins where the polarisation is reduced by 30-40%as compared to the totally polarised state. The binding energy is equal to approximately 0.5 eV. Increasing doping of the CuO2 plane leads to a statistical distribution of formed clusters; above a critical concentration a percolation network is generated. This network is characterised by high mobility of O holes, whereas Cu spins are almost totally localised. Their polarisation decreases with increasing network doping. In this way a microscopic electronic phase separation into charge-depleted antiferromagnetically correlated and charge-enriched quasimetallic domains are formed