| Autor: |
D. Wohlleben, H. Broicher, E. Braun, W. Schnelle, O. Hoffels |
| Rok vydání: |
1992 |
| Předmět: |
|
| Zdroj: |
Physics and Materials Science of High Temperature Superconductors, II ISBN: 9789401050869 |
| Popis: |
We present high resolution measurements of the specific heat and of the thermal expansion of well characterized samples of three different classes of the high Tc superconductors (HTSC), namely of La-Sr-Cu-O, Y-Ba-Cu-O and Bi- and TI-2212 and -2223. At the Tc of all these samples we observe specific heat anomalies. In the case of La-Sr-Cu-0 the anomaly can be described by a broadened mean field step, while the anomaly of Y-Ba-Cu-0 is modified by a contribution from (gaussian) fluctuations of the superconducting order parameter. These fluctuations are threedimensional (3D) near Tc and show a crossover to 2D-behaviour ≈ 20 K from Tc. The anomalies of the Bi and Tl high Tc superconductors have very little similarity with a mean field jump. The analysis of these anomalies gives evidence for strong 2D-gaussian fluctuations further away from Tc and a changeover to critical fluctuations within ≈ ±5 K around Tc . The thermal expansion anomalies of the HTSC are strongly anisotropic. From a combination of both measurements we give estimates for the uniaxial or hydrostatic pressure dependencies dTc/dpi|T=Tc. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
|
