Loss of superconducting phase coherence in YBa(2)Cu(3)O(7) films: vortex-loop unbinding and Kosterlitz-Thouless phenomena.
The linear conductance G' + iG(") parallel to the CuO(2) planes of flat d = 50-600 nm thin films is measured between 30 mHz and 800 kHz. The decay of the phase-coherent superfluid density signals the proliferation of 3D vortex loops which terminates at T*<T(c), where omegaG"(T*) attains 35(5) nH(-1) being independent of d. We ascribe this novel transition to the blowout of loops which reach the film thickness. Above T(c), G(omega) appears to be determined by unbound vortex lines thermally excited in a 2D phase-incoherent superfluid showing features previously being associated with a Kosterlitz-Thouless transition.
Kötzler
J
J
Institut für Angewandte Physik und Zentrum für Mikrostrukturforschung, Universität Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany.
Görlitz
D
D
Skwirblies
S
S
Wriedt
A
A