Strong-coupling effects on the temperature dependence of penetration depth inYBa2Cu3O7−δthin films nearTc

Abstract

We present accurate experimental data on the temperature dependence of the penetration depth \ensuremath{\lambda} in $c$-axis-oriented ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ thin films close to ${T}_{c}.$ The samples were grown in situ on ${\mathrm{LaAlO}}_{3}$ (100) single-crystal substrates. The penetration depth measurements are performed by an inverted microstrip method, using resonators of different geometries. Near ${T}_{c}$ we compare the three-dimensional (3D) $\mathrm{XY}$ critical regime and the Ginzburg-Landau (GL) behavior. Our data show that the GL approach follows the observed temperature dependence closer than the 3D $\mathrm{XY}$ model. The experimental results are discussed in the light of recent models describing the effect of strong coupling on the $\ensuremath{\lambda}(T)$ behavior near ${T}_{c}$ for an $s$-wave and a $d$-wave high-temperature superconductor.