We have measured the noise spectrum near the transition temperature of the high-T, superconductor YBa~Cu307 q thin film which shows a rather broad transition temperature width with the onset transition temperature T, ,"", = 90 K and the zero-resistance temperature T, ""=30 K. We observed two noise peaks, one near the onset transition temperature (81 K) and another one near the zero-resistance temperature (45 K). These two noise peaks show distinctively different dependences on the magnetic field and driving current. Furthermore, the frequency dependence of the noise spectrum at 81 K shows 1/f behavior while that of the noise spectrum at 45 K shows 1/f "+ ' behavior with o. approaching 1, as the magnetic field is increased. The noise peak near the zeroresistance temperature region is believed to be due to the noise associated with the motion of free vortices.
Single-phase Yl Ba2Cu309 -"has been synthesized and characterized. Although x-ray diffraction shows only the Yl Ba2Cu309 -"phase which has an orthorhombically distorted perovskite structure, resistance measurements reveal two transition temperatures, T, l =95.5 K and T,2 =93 K. Thermoelectric power measurements indicate that YlBa2Cu309is of n type.Strong enhancement and unusual temperature dependence for the "phonon-drag" effect which might be indicative of an unusual superconducting mechanism in this material have been observed.
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