Published online by Cambridge University Press: 28 February 2011
The discovery of superconductivity above liquid nitrogen temperature in copper oxide compounds has resulted in much research activity aimed at understanding the nature of these materials, as well as at using them in practical devices from sensors to levitated trains. Despite this intense interest, there have been relatively few studies of fluctuation phenomena in them. One fluctuation-induced property of interest is the electrical noise power spectrum. Although excess noise above the thermal background in metals is usually observable only in thin films, we report here measurements of significant noise power in bulk composite samples of the nominal 90K superconductors Y1Ba2Cu3O7-δ (YBCO) and Er1Ba2Cu3O7-δ (EBCO) from 77K to 290K. The “excess” noise spectrum (the total spectrum minus the frequency-independent amplifier and thermal noise contributions) is 1/f in shape in the normal state; no 1/f noise is observed while superconducting. The excess noise magnitude is found to be too large to originate from the expected number of charge carriers, and to have an unusual temperature dependence. We discuss two possible explanations for these observations.