Local pairs in high-temperature superconductors: proof of existence and manifestation in heat transfer

The comparison of the temperature anomalies of the charge carrier density in high-temperature cuprate superconductor Bi$_{1.6}$(Pb$_{0.4})$Sr$_2$Ca$_2$Cu$_3$O$_{10+x}$ and features of the parameters of the crystal lattice has demonstrated that the concept of pairing of single-particle hole excitations on the Fermi surface into singlet pairs is realistic. Anomalies of the thermal conductivity correlated with the presence of paired quasiparticle states have been revealed. Both types of anomalies indicate the existence of three stages of the temperature evolution of a pseudogap.