Images from IBM Scanning SQUID Microscope Group

C.C. Tsuei et al., Phys. Rev. Lett. 73, 593 (1994).

J.R. Kirtley et al., Nature 373, 225 (1995).

nature.gif

Here is a beautiful false color scanning SQUID image (red=high B, blue=low B) from John Kirtley, Chang Tsuei and Mark Ketchen of IBM showing the magnetic field in four split YBCO rings. Only the central ring is composed of three junctions, such that in a d-wave superconductor, the three crystal interfaces would lead to a net phase shift of 180 degrees around the ring. This leads to spontaneous currents creating a 1/2 quantum of flux in the ring, as observed.

spinnat.gif

Has side-by-side images of 2 tricrystal ring samples with two geometries, the left which should show the 1/2 flux quantum effect in the center ring for a d-wave superconductor, the right which should not for any gap function with inversion ( x = -x, y = -y ) symmetry. The left does, the right doesn't. Also from Nature paper.

mixed.gif

Shows the d-wave symmetry tricrystal ring sample, cooled down in a field of about 15 mG, such that the control 0-junction ring has 3 flux quanta in it, the 2 2-junction rings each have 2 flux quanta in them, and the 3-junction ring in the center has 1 1/2 flux quanta in it. This image was included in the conference proceedings for the Miami conference.

blanket.gif (Kam's zoo)

Shows a blanket coverage of YBCO on a d-wave symmetry tricrystal substrate, cooled in a few mG field. There are 7 bulk vortices, 4 Josephson vortices along the horizontal and diagonal grain boundaries (they are elongated), and a half Josephson vortex at the tricrystal point.
Images courtesy of J. Kirtley / kirtley@watson.ibm.com
Maintained by Peter Hirschfeld / pjh@phys.ufl.edu / Last modified: Nov. 8, 1995.