CPM Seminar

The Superconducting Quantum Interference Device (SQUID) is the most sensitive detector of magnetic fields known. We have built a microscope that scans a pickup loop that is an integral part of a specially designed SQUID relative to a sample. This microscope can image a few tenths of a microgauss, a few hundred Bohr magnetons of spin, or a few nanoamps of current, with a spatial resolution of a few microns. We have used this microscope to image magnetic vortices that have exactly half the conventional magnetic flux quantization, in specially designed tricrystal samples of the high-T_c cuprate superconductors. By varying the sample geometry, we have shown that this half-flux quantum effect is indicative of the underlying symmetry of the Cooper pairing, and that a number of the high-T_c hole-doped cuprates have d-wave symmetry. By imaging the elliptical shape of vortices trapped between the highly conducting planes of the organic and cuprate superconductors, we have shown that the Cooper pair tunneling between planes is weaker than required by the interplane tunneling model of superconductivity in these materials.

Thursday, January 22nd 1998, 15:30
Ernest Rutherford Physics Building, room 114