Magnetic-field induced finite-size effect in the high-temperature superconductor YBa2Cu3O7-d: an analogy to rotating 4He

R. Lortz1,2, C. Meingast1, A.I. Rykov3, T. Masui3 und S. Tajima3
1Forschungszentrum Karlsruhe, Institut für Festkörperphysik, 76021 Karlsruhe, Germany
2Fakultät für Physik, Universität Karlsruhe, 76131 Karlsruhe, Germany
3ISTEC, 10-13 Shinonome I-Chome, Koto-ku, Tokyo 135, Japan

There is presently a great deal of interest in the effect of high magnetic fields on superconductivity, the pseudogap and on the AF-magnetic fluctuations in high-Tc superconductors. We have studied the response of the superconducting transition and the associated superconducting fluctuations in untwinned YBa2Cu3Ox single crystals to magnetic fields up to 10 T using high-resolution dilatometry, which was previously shown to be extremely useful in characterizing the zero-field transition. We show that the broadening of the superconducting transition in a magnetic field is a consequence of a finite-size scaling effect due the additional vortex-vortex length scale, which prevents the divergence of the coherence length at Tc. The behavior is analogous to that of the superfluid transition in rotating superfluid 4He [1]. Apart from this broadening, practically no field effect is observed on superconductivity and on superconducting fluctuations, which we observe up to about 30 K above Tc. [1] R. Haussmann, PRB 60, S. 12373 (1999).