Recent evidence of three-dimensional xy-critical behavior in the Meissner phase of cuprate superconductors strongly suggests that, close to the transition temperature, the fluctuations of the order parameter are
essentially those of a neutral superfluid or xy-model. Full confirmation of xy-behavior requires the sound waves of the superfluid to dominate the low-temperature properties. Our calculation of the sound wave contribution to the magnetic penetration depth, which yields lambda (T)/lambda (0)=1+AT**4 in the limit T -> 0, is in remarkable agreement with recent experiments. Thus, thermal fluctuations not only mediate 3D-xy-critical point behavior
but dominate the entire finite temperature behavior in the ordered state. The nature of the superconducting state in the cuprates then appears to be essentially that of superfluidity.
By: T. Schneider and M. H. Pedersen
Published in: RZ2572 in 1994
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