Noise sources across a normal-to-superconducting boundary in bulk YBa/sub 2/Cu/sub 3/O/sub 7-x/

Experiments in which a normal-to-superconducting (NS) boundary is created in an originally superconducting bar of bulk YBa/sub 2/Cu/sub 3/O/sub 7-x/ is described. The first noise measurements associated with such a boundary are presented. A high-density (5.20 g-cm/sup -3/) sample (sample A) and a low density (4.23 g-cm/sup -3/) sample (sample B) have been investigated. Common to both samples is 1/f/sup 2/ noise observed in the frequency region between about 15 and 50 Hz that can be associated with the NS boundary itself. Sample A also exhibits conventional 1/f noise as expected for the normal part of the boundary, below about 15 Hz. In contrast, sample B shows 1/f/sup 1.5/ noise in this region; since the sample contains considerably fewer small grains than sample A, any 1/f noise is presumably masked in B. It is suggested that the 1/f/sup 2/ noise might be associated with flux-flow noise.<
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