The Temperature Echo of the Superconducting Phase Transition

Abstract

An analysis of experimental heat capacity at $T>T_{c}$ is presented for series of samples $(R)Ba_2Cu_3O_{6+x}$ (with $x$ close to optimal). For all samples the anomaly was discovered which occurred steadily in the interval 250-290 K (anomaly $T_{h}$). The anomaly $T_{h}$ looks like a phase transition anomaly. It was shown that the anomaly $T_{h}$ correlates with superconducting anomaly $T_c$, temperatures $T_{h}$ and $T_{c}$ being connected by the ratio $T_{h}\approx 3T_c$. The anomaly $T_{h}$ is interpreted as the origination of pairing the charge carriers. Anomalies at $T\approx 3T_c$ were also detected in heat capacity of low temperature superconductors $Hg$ and $Nb_3Ge$.