Europhys. Lett.
Volume 67, Number 5, September 2004
Page(s) 834 - 839
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 01 August 2004
Europhys. Lett., 67 (5), pp. 834-839 (2004)
DOI: 10.1209/epl/i2004-10108-7

Evidence for a bulk complex order parameter in $\chem{Y_{0.9}Ca_{0.1}Ba_2Cu_3O_7}$ ${_{-\delta}}$ thin films

E. Farber1, 2, G. Deutscher1, B. Gorshunov3, 4 and M. Dressel3

1  School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Science, Tel Aviv University - Ramat Aviv 69978, Israel
2  Department of Electrical and Electronic Engineering College of Judea and Samaria - Ariel, Israel
3  1. Physikalisches Institut, Universität Stuttgart Pfaffenwaldring 57, D-70550 Stuttgart, Germany
4  General Physics Institute, Russian Academy of Sciences - Moscow, Russia

(Received 27 February 2004; accepted in final form 15 June 2004)

We have measured the penetration depth of overdoped $\chem{Y_{0.9}Ca_{0.1}Ba_2Cu_3O_7}$ ${_{-\delta}}$ ( $\chem{Ca}$- $\chem{YBCO}$) thin films using two different methods. The change of the penetration depth as a function of temperature has been measured using the parallel-plate resonator (PPR), while its absolute value was obtained from a quasi-optical transmission measurement. Both sets of measurements are compatible with an order parameter of the form $\Delta_{d_{x^2-y^2}}+{\rm i}\delta_{d_{xy}}$, with $\Delta=14.5\pm
1.5$ $\un{meV}$ and $\delta=1.8$ $\un{meV}$, indicating a finite gap at low temperature. Below 15 $\un{K}$, the drop of the scattering rate of uncondensed carriers becomes steeper in contrast to a flattening observed for optimally doped $\chem{YBCO}$ films. This decrease supports our results on the penetration depth temperature dependence. The findings are in agreement with tunneling measurements on similar $\chem{Ca}$- $\chem{YBCO}$ thin films.

74.20.Rp - Pairing symmetries (other than s-wave).
74.72.Bk - $\chem{Y}$-based cuprates.
78.66.-w - Optical properties of specific thin films.

© EDP Sciences 2004