EXPERIMENTAL-EVIDENCE OF A DIMENSIONAL CROSSOVER IN Y1BA2CU3O7-SIGMA

High-resolution torque-magnetometry data have been obtained on an untwinned single crystal of Y1Ba2Cu3O7- in the temperature range 63<T<88 K (Tc=90.5 K). At T=80 K and above, the data are fitted extremely well with the accepted three-dimensional phenomenological theory, but below this temperature an anomalous torque develops when the magnetic field lies close to the Cu-O planes. The qualitative and quantitative features of our results provide strong evidence that breakdown of the three-dimensional description below 80 K is associated with a crossover to two-dimensional superconducting behavior. © 1990 The American Physical Society.