Magnetic and thermal properties of high Tc superconductors

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1990
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Lee, Wonchoon
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David C. Johnston
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Physics and Astronomy
Physics and astronomy are basic natural sciences which attempt to describe and provide an understanding of both our world and our universe. Physics serves as the underpinning of many different disciplines including the other natural sciences and technological areas.
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Abstract

Measurements of the normal state magnetic susceptibility [chi](T) of YBa2Cu3O7, Bi1.8Pb0.2Sr2CaCu2O8+[delta], and Bi2- xPb xSr2Ca2Cu3O10+[delta] (x = 0.2 and 0.25) were carried out. All [chi](T) data show negative curvature below ~ 2T c. The data for YBa2Cu3O7 are in excellent agreement with a new calculation of the superconducting fluctuation and diamagnetism. From the analysis, we infer s-wave pairing and microscopic parameters are obtained. For [chi](T) of YBa2Cu3O7, part of the negative curvature is inferred to arise from the normal state background. We find a strong temperature dependent anisotropy [delta][chi] ≡ [chi] c - [chi] ab and estimate the normal state spin contributions to [chi](T). The heat capacity C(T) of YBa2Cu3O7 is reported for 0.4 K < T < 400 K in zero and 70 kG magnetic fields. In addition to the feature associated with the onset of the superconductivity at T c, two anomalies in C(T) were observed near 74 K and 330 K, with another possible anomaly near 102 K; the temperatures at which they occur correlate with anomalies in [chi](T) and ultrasonic measurements. The occurrence of the anomaly at ~eq330 K is found to be sample-dependent. The influences of a magnetic field and the thermal and/or magnetic field treatment history dependence of a pellet sample on C(T), the entropy and the influence of superconducting fluctuations on C(T) near T c, and the possible source of the observed intrinsic nonzero [gamma](0) at low T are discussed.

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Mon Jan 01 00:00:00 UTC 1990