HALL ANGLE EVIDENCE FOR THE SUPERCLEAN REGIME IN 60K YBA2CU3O6+Y

A type-II superconductor is in the ''superclean'' regime when the spacing h omega(0) between energy levels in the vortex core greatly exceeds the width of the levels h/tau. A key signature of this regime is a flux-flow Hall angle theta H that approaches +/-pi/2. We report the first observation of this trend in a high-temperature superconductor. In ''60 K'' YBa(2)CU(3)0(6+y) crystals, \tan theta(H)\ is observed to increase dramatically when the temperature decreases below similar to 40 K, attaining the magnitude 0.85 at 15 K. By extrapolation, we estimate that omega(0) tau increases to 2-3 at 3 K. Below 40 K, the Hall conductivity sigma(xy) is negative and decreases as 1/H at high fields.