PACS. 07.57.c Infrared, submillimeter wave, microwave and radiowave instruments, equipment and techniques - 74.72.h High-Tc compounds - 74.76.w Superconducting films
Springer Online Journal Archives 1860-2000
Abstract: Measurement of the penetration depth as a function of temperature using millimeter wave transmission in the range 130-500GHz are reported for three (YBCO) laser ablated thin films. Two films, deposited on a substrate ( ), exhibit a narrow resistive transition ( ). One has been subsequently irradiated with ions in order to increase the scattering rate of the quasi-particles ( ). The third film, grown on MgO ( ), exhibits also a fairly narrow transition ( ) and a high crystalline quality. The experiment provides the absolute value for the penetration depth at low temperature: the derivation from the transmission data and the experimental uncertainty are discussed. We find a zero temperature penetration depth Å, Å and Å, for YBCO-500 Å/ (pristine), YBCO-1300 Å/MgO and YBCO-500 Å/ (irradiated) respectively. exhibits a different behavior for the three films. In the pristine sample, shows a clear temperature and frequency dependence, namely the temperature dependence is consistent with a linear variation, whose slope decreases with frequency: this is considered as an evidence for the scattering rate being of the order of the measuring frequency. A two fluids analysis yields .In the two other samples, does not display any frequency dependence, suggesting a significantly larger scattering rate. The temperature dependence is different in these latter samples. It is consistent with a linear variation for the YBCO/MgO sample, not for the YBCO/ irradiated one, which exhibits a T2 dependence up to . We have compared our data to the predictions of the d-wave model incorporating resonant scattering and we do not find a satisfactory agreement. However, the large value of in the pristine sample is a puzzle and sheds some doubt on a straightforward comparison with the theory of data from thin films, if considered as dirty d-wave superconductors.
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