Scanned probe microscopes image magnetic fields with excellent sensitivity but (by modern standards) modest spatial resolution. I will briefly review and compare some of these techniques, and then talk about some applications of scanning SQUID and Hall bar microscopies to fundamental research. The best known of these applications was the observation of vortices with exactly half of the conventional quantum of total magnetic flux in special geometries involving the high critical temperature superconductor YBa2CuO3 (YBCO). Recently technological advances have allowed us to use the half-flux quantum effect to determine with remarkable precision at what angles (relative to the crystalline axes) the superconducting wave function passes through zero in YBCO. If time permits I will also explain how scanning magnetic microscopy has been used to develop rules for eliminating flux trapping in superconducting electronic devices, and for making current-voltage measurements on the femtovolt scale.
Coffee and cookies before the presentation at 3:15 pm, and refreshments after the presentation will both be served in Room 128.