高温氧化物超导体于T＞T_c区域的比热奇异可能探讨

Specific-Heat Properties of High-T_c Oxide Superconductors at T>T_c

该文利用微机自动控制的比热扫描法测量系统对高Ｔｃ氧化物超导体ＹＢａ２Ｃｕ３Ｏ７－δ、ＢｉＳｒＣａＣｕＯ及ＴＩＢａＣｈＣｕＯ从液氮温度到室温进行了详细的比热测量．实验发现除临界温度处的正常－超导转变外这三个系列超导体在Ｔｃ＜Ｔ＜ＴＲＯＯＭ（室温）区域还存在负的比热反常峰．这类反常峰的形状类似于倒置的λ相交，峰的位置和个数与样品的受热历史有关．另外，实验证明存在一个临界的最高热循环温度ＴＣＴＣ，当样品的最高热循环温度ＴＣＴ小于ＴＣＴＣ时，这类比热异常峰将不会出现．对应于ＹＢＣＯ、ＢＳＣＯＯ、ＴＢＣＣＯ．实验确定的该临界温度ＴＣＴＣ分别为２５８±３Ｋ、２３８Ｋ±２Ｋ、２６１Ｋ±１Ｋ．

Specific-heat measurements of high-Tc superconductors YBa2Cu3O7-δBiSrCaCuO and TlBaCaCuO were made in detail from LN2 temperature to room temperature by the sweep method. Besides the specific-heat jump at Tc of the normal state to superconductive state to superconductive state,teh experiments found thatt negative and sharp specific-heat anomalies with the shape of upended λ-like transition existed in these three groups of oxide superconductros.Some characters,e. G.anomaly temperature and number of these anomaly peaks were ralated to heated history of the samples.Meanwhile,the experiments showed that there exised a critical maximum thermal-cycle temperature TCTC When the maximum thermal-cycle temperature TCTC was lower than TCTC,esuch anomalies would be disappeared.The values of TCTC were 258±2K,238±2Kand 261±1K, respectively ofr YBCO, BSCOO.The paper also gave some disussion ablout the possible relationship between these anoma lies and the superconductivity of the high0Tc superconducting oxides.