# Evidence of 3D-XY Critical Behavior in La(sub2-x)Sr(subx)CuO(sub4) Films

We report measurements of the `zero field' ac sheet impedance $Z = R + i \omega L_k$ for thin, $c$-axis-oriented La$_{2-x}$Sr$_x$CuO$_4$ films. For sufficiently thin films of thickness $d$, the magnetic penetration depth $\lambda_{ab}$ is given by $L_k = \lambda_{ab}^2 / d$. We find that the temperature and intriguing doping dependence of $L_k$ as well as the amplitude of the perpendicular real-space phase correlation length $\xi_{\rm c 0}^{\varphi}$ are fully consistent with the critical behavior of the three-dimensional XY model and finite size scaling. Moreover, invoking finite size scaling, we determine the value of the critical amplitude of $\xi_{\rm c 0}^{\varphi}$. (Dept480)

By: Y. Jaccard, T. Schneider, J. P. Locquet, E. J. Williams, P. Martinoli (Univ. de Neuchatel, Switz.) and O. Fischer (Univ. de Geneve, Switz.)

Published in: Europhysics Letters, volume 34, (no 4), pages 281-6 in 1996

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