Bi系与Tl系高T_c超导体的比热奇异研究

Specific-heat Anomaly in High-Tc Superconductors of Bi- and Tl-System

利用扫描比热法对Ｂｉ－Ｓｒ－Ｃａ－Ｃｕ－Ｏ和Ｔｌ－Ｂａ－Ｃａ－Ｃｕ－Ｏ超导体从液氮温度到室温作了详尽的比热测量．类似于ＹＢＣＯ超导体，在临界转变温度与室温的这一区间里发现Ｂｉ系和Ｔｌ系样品也存在负的比热奇异行为，即存在形状类似于倒置λ相变的比热反常峰．反常峰的位置和数量与样品的受热历史有关．并且实验发现存在一个临界的最高热循环温度Ｔ（ＣＴＣ），当样品的最高热循环温度Ｔ（ＴＣ）小于Ｔ（ＣＴＣ）时，这类反常峰将消失．对ＢＳＣＣＯ和ＴＢＣＣＯ这一临界热循环温度Ｔ（ＣＴＣ）分别为２３８±２Ｋ和２６１±１Ｋ．

Specific-heat measurements were made in high temperature superconductors of Bi- and Tl-system by the sweep method from liquid nitrogen temperature to room temperature. Similar to YBCO, negative specific-heat jumps with the shape of upended λ-like transition are detected in these two systems above the critical transition temperature. The number and the position of these anomaly peaks are related to heat history of the samples. Experimental results show that there is a critical maximum thermal-cycle temperature TCTC. When the maximum thermalcycle temperature TTc of the samples is less than TCTC, such anomalies will disappear. The values of TCTC for BSCCO and TBCCO are 238±1 K and 261±1 K respectively.