Abstract
We report measurements of the "zero field" ac sheet impedance Z = R + iωLk for thin, c-axis–oriented La2 − xSrxCuO4films. For sufficiently thin films of thickness d, the magnetic penetration depth λab is given by Lk = λab2/d. We find that the temperature and intriguing doping dependence of Lk as well as the amplitude of the perpendicular real-space phase correlation length ξc0φ are fully consistent with the critical behaviour of the three-dimensional XYmodel and finite-size scaling. Moreover, invoking finite-size scaling, we determine the value of the critical amplitude of ξc0φ.