Temperature dependence of the penetration depth of yba₂cu₃o_7-δ films near t_c

The temperature dependence of the penetration depth, λ of films of YBa₂Cu₃O_7-δ measured using radio frequency techniques, has been found to have a mean-field-like exponent well within some estimates of the critical region. This result is found only if finite-size boundary conditions at the film edge are included in the analysis. This observation agrees with a recent renormalization group calculation in which the critical exponent for λ is mean-field-like, while the others are YY-like. It could also imply that the critical regime has not been reached, but then recent heat capacity measurements with AY-like behavior would have to be flawed.