CAJ | 학술논문

本研究在制备出系列掺杂的高质量氧化物超导体单晶Bi_2Sr_(2-x)La_xCuO_6的基础上,开展了系统的比热测量工作,发现欠掺杂的高温超导体的比热跳变高度很矮,远远低于BCS理论预言的值,而且越到欠掺杂,比热跳变高度越矮.有趣的是,在转变温度以上很高的温区仍然有一个长长的尾巴,所计算的熵在超导转变温度处不守恒.此外,当把超导转变以上的部分均考虑在内时,熵会自动守恒.联想到从过掺杂到欠掺杂的连续过渡规律,可以认定,欠掺杂的样品在远远高于超导转变温度的区域已经存在电子库珀对.
본연구재제비출계렬참잡적고질량양화물초도체단정Bi_2Sr_(2-x)La_xCuO_6적기출상,개전료계통적비열측량공작,발현흠참잡적고온초도체적비열도변고도흔왜,원원저우BCS이론예언적치,이차월도흠참잡,비열도변고도월왜.유취적시,재전변온도이상흔고적온구잉연유일개장장적미파,소계산적적재초도전변온도처불수항.차외,당파초도전변이상적부분균고필재내시,적회자동수항.련상도종과참잡도흠참잡적련속과도규률,가이인정,흠참잡적양품재원원고우초도전변온도적구역이경존재전자고박대.
Our group has measured the magnetic field and temperature dependence of specific heat on Bi_2Sr_(2-x)La_xCuO_6 single crystals in wide doping and temperature regions. The superconductivity related specific heat coefficient γ_(sc) and entropy S_(sc) are determined. It is found that γ_(sc) has a hump-like anomaly at T_c and behaves as a long tail which persists far into the normal state for the underdoped samples, but for the heavily overdoped samples the anomaly ends sharply just near T_c. Interestingly, we found that the entropy associated with superconductivity is roughly conserved when and only the long tail part in the normal state is taken into account for the underdoped samples, indicating the residual superconductivity above T_c.