Fine effects in the temperature dependence of the thermal conductivity of Y-123 cuprates in a “weak” pseudogap state

Quasiregular anomalies of the thermal conductivity $k$ of the YBa$_2$Cu$_3$O$_{7-x}$ hole high-temperature superconductor in a pseudogap state, as well as a “giant” anomaly near $T_{\mathrm{C}}$, have been detected for the first time. The temperature anomalies of the carrier density ($n^{\mathrm{h}}$) in YBa$_2$Cu$_3$O$_{7-x}$ have been revealed and their correlation with $k$ anomalies has been established. It has been shown that $n^{\mathrm{h}}(k)$ anomalies of the pseudogap state are due to the step-by-step pairing of charge carriers into positively charged bosons. The correlation of $n^{\mathrm{h}}(k)$ anomalies near $T_{\mathrm{C}}$ with the topological conversion of a part of the Fermi surface, on one hand, and with the structure anomaly, on the other hand, has been established.