https://doi.org/10.1140/epjb/e20020046
Low temperature dependence of the penetration depth in YBCO thin films revisited by mm wave transmission and surface impedance measurements
1
Laboratoire de Physique de la Matière Condensée, École Normale
Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France
2
School of Physics and Astronomy, Raymond and Beverly Sackler Faculty
of Exact Science,
Tel Aviv University, Ramat Aviv 69978, Israel
3
THALES Research and Technology, 91404 Orsay, France
4
Unité Mixte de Physique CNRS/THALES, 91404 Orsay, France
Corresponding author: a nicole.bontemps@espci.fr
Received:
7
May
2001
Revised:
18
October
2001
Published online: 15 February 2002
We report results obtained with two different experimental set-ups in
state-of-the-art YBCO thin films as similar as possible, prepared by pulsed
laser deposition on LaAlO3 substrates: a surface impedance
measurement on 4000 Å thick films using a parallel
plate resonator (10 GHz), and a far infrared transmission (100–400 GHz)
measurement which requires thinner (1000 Å) samples. The former
measurement yields the temperature variation of the penetration depth
and the real part of the conductivity, provided the absolute value of
is known. The latter yields
the imaginary part of the conductivity, hence the absolute value
of the penetration depth, as well as its temperature dependence at the
measuring frequency. Combining these two experiments, we
establish a quasi-linear temperature variation of , with a
2 Å K-1 low temperature slope, and a fairly large zero temperature
value 
=(1800±200) Å . The scattering
rate of the quasi-particles calculated from a two-fluids model shows that the
films compare to good quality single crystals, where twice a larger slope
has been found. This surprising behavior is described in detail,
including an in-depth structural analysis of the samples in order to
evaluate their similarities. We find that the 10 GHz data obtained in the thickest
films can be fitted to
the dirty d-wave mode in the unitarity limit, with an extrapolated slope of
3 Å K-1, but yield a scattering rate that is difficult to reconcile with the
high Tc (92 K) of the films.
PACS: 74.25 Nf – Response to electromagnetic fields (nuclear magnetic resonance, surface impedance, etc.) / 74.76 Bz – High-Tc films / 78.66 -w – Optical properties of specific thin films
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2002
