THE dynamics of trapped vortices of magnetic flux in the high-Tc oxide superconductors have been much studied1-4, but remain poorly understood; in particular, we have much to learn about vortex 'creep' at low temperatures. Using a scanning Hall micro-probe to measure directly the spatial and temporal variation of the flux density in YBa2Cu 3O7 single crystals, we have uncovered a remarkable asymmetry in the magnetization profile, which is induced by the direction of the field (applied normal to the a-b crystal face). The external field imparts a rotation to the vortex motion, which strongly distorts the remanent profile away from the form predicted by conventional critical-state models5. This rotation was not anticipated and, to our knowledge, is not accounted for in existing theories.
All Science Journal Classification (ASJC) codes