Kathryn A. Moler, ^* John R. Kirtley, D. G. Hinks, T. W. Li, Ming Xu

The strength of the interlayer Josephson tunneling in layered superconductors is an essential test of the interlayer tunneling model as a mechanism for superconductivity, as well as a useful phenomenological parameter. A scanning superconducting quantum interference device (SQUID) microscope was used to image interlayer Josephson vortices in Tl₂Ba₂CuO₆₊ and to obtain a direct measure of the interlayer tunneling in a high-transition temperature superconductor with a single copper oxide plane per unit cell. The measured interlayer penetration depth, _c, is ~20 micrometers, about 20 times the penetration depth required by the interlayer tunneling model.

K. A. Moler, Department of Physics, Princeton University, Princeton, NJ 08544, USA.
J. R. Kirtley, IBM T. J. Watson Research Center, Post Office Box 218, Yorktown Heights, NY 10598, USA.
D. G. Hinks and T. W. Li, Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA.
M. Xu, James Franck Institute, University of Chicago, Chicago, IL 60637, USA.
^*   To whom correspondence should be addressed.

   Present address: Lucent Technologies, 2000 North Naperville Road, Naperville, IL 60566, USA.