Evidence for a bulk complex order parameter in thin films

E. Farber; G. Deutscher; B. Gorshunov; M. Dressel

doi:10.1209/epl/i2004-10108-7

All issues

Volume 67 / No 5 (September 2004)

Europhys. Lett., 67 5 (2004) 834-839

Abstract

Issue		Europhys. Lett. Volume 67, Number 5, September 2004


Page(s)		834 - 839
Section		Condensed matter: electronic structure, electrical, magnetic, and optical properties
DOI		https://doi.org/10.1209/epl/i2004-10108-7
Published online		01 August 2004

Europhys. Lett., 67 (5), pp. 834-839 (2004)

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: 15 June 2004

Abstract

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.

PACS: 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

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