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Phys. Rev. B 54, R9674–R9677 (1996)

Absence of a Kosterlitz-Thouless transition in ultrathin YBa2Cu3O7-δ films

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J. M. Repaci, C. Kwon, Qi Li, Xiuguang Jiang, T. Venkatessan, R. E. Glover, III, and C. J. Lobb
Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, Maryland 20742

R. S. Newrock
Department of Physics, University of Cincinnati, Cincinnati, Ohio 4521-0011

Received 17 May 1996; revised 8 July 1996; published in the issue dated 1 October 1996

We have performed nanovolt-level dc measurements on single-unit-cell films of YBa2Cu3O7-δ. When only the low-sensitivity data are analyzed, they are roughly consistent with the occurrence of a Kosterlitz-Thouless transition. At the lowest currents and voltages, however, the samples are ohmic at temperatures quite far below the nominal Kosterlitz-Thouless transition temperature, contrary to the theory. The ohmic response at low currents implies that there are unbound vortices present well below the nominal Kosterlitz-Thouless transition temperature.

© 1996 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevB.54.R9674
DOI:
10.1103/PhysRevB.54.R9674
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