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Sample Characteristics

A mosaic of three twinned single crystals of $\mbox{YBa$_{2}$ Cu$_{3}$ O$_{6.95}$ }$ were utilized in this experiment. The $\mbox{YBa$_{2}$ Cu$_{3}$ O$_{6.95}$ }$ crystals were of extremely high quality, as characterized by low-field magnetization, ab-plane resistivity, microwave surface resistance and heat capacity measurements [85]. For example, the superconducting transition temperature Tc, determined by magnetization measurements was found to be 93.2K with a relatively narrow transition width $\Delta T_{c} < 0.25$K.

The $\mbox{YBa$_{2}$ Cu$_{3}$ O$_{6.95}$ }$ single crystals were grown by a flux method in yttria-stabilized zirconia crucibles. CuO-BaO flux was poured over hot (950- $970^{\circ}$C) crystals initially grown from high purity Y2O3 ($99.999 \%$), CuO ($99.999 \%$) and BaCO3 ($99.997 \%$) compounds. To ensure each crystal had the identical oxygen concentration corresponding to the maximum Tc, all three crystals were carefully annealed prior to the experiment. For 3 days the crystals were held in 1 atmosphere of O2 at $860^{\circ}$C, followed by 14 days at $450^{\circ}$C before rapidly cooling to room temperature. Together the three crystals had a total mass of 53mg.

Jess H. Brewer