Physica B 165&166 (1990) 1377-1378 North-Holland RESISTANCE NOISE AT THE SUPERCONDUCTING TRANSITION IN THICK FILMS OF YBa2CuS07-o' J. M. Aponte, G. Gutierrez and M. Octavio Centro de Ffsica. Instituto Venezolano de Investigaciones Cientlficas (I.V.I.C.). Apartado 21827. Caracas 1020A. Venezuela. Measurements of the power spectral density of the resistance noise were performed in thick films of with broad superconducting tr:r,nsitions and in the frequency range from 0.1 Hz to 100rfz. The normalized power spectrum (S IV ) of the excess noise depends on frequency as 1/f a , with a=1 over a wide range of temperature. We have also found that ft the transition, the magnitude of this excess noise shows peaks at the same temperatures at which R- (dR/dT) has peaks and also very close to the temperature at which the sample reaches its R=O state. Possible sources of noise responsible for these effects are proposed. Experiments on the resistance noise of copper-oxide based superconductors show that the excess noise, which exhibit a 1/f-type spectrum, has a high level, in both bulk samples(1) and thin films(2,S), as compared to the noise in classical superconductors. These results have implications for the practical applications of these ceramics. On the other hand it is of interest to understand the origin of such excess noise. All the results found in the literature agree that the excess noise is zero in the superconducting state and that it rises sharply at the transition. This behavior is not yet well undestood. In this paper we study the power spectrum of the resistance noise near the superconducting transition of thick films of YBa2Cu307_o with broad resistive transitions. The transition is approached by either changing the temperature at a constant current or by changing the current at a constant temperature. Our films are about 1 thick and were prepared on various types of substrates: Zr(Ca)02' alumina and sapphire. The details of the fabrication of our samples have been reported elsewhere(4). In order to measure the resistance noise we use a four-probe configuration. A d.c. current is applied to the sample and the signal between the voltage contacts is coupled through a transformer into a PAR113 amplifier in series with a home-made low-pass filter (cut-off frequency of 1kHz), the output of which is measured by a spectrum analyzer model HP3582A controlled by a microcomputer. The background noise is measured and subtracted in order to obtain the current-dependent excess noise. The sample is attached to a copper block inside a brass can which is inmersed in a liquid nitrogen or liquid helium bath. The temperature can be varied by pumping on the bath and/or applying current to a heater, controlled by a temperature controller. The power spectral density Sv of our samples exhibit 1/f a behavior, with a=1, except near Tconset, the temperature at which the resistance starts to drop, there we fou nd that a> 1. Figure 1 shows the magnitude of SvIV2 at f=10Hz, normalized to its value at room temperature, as a function of temperature for one of our samples with room temperature resistance of 7.2 n. We observe two peaks at the same temperatures at which W 1 dR/dT has peaks, also shown in the same figure. Similar behavior was also observed in other samples. This result suggests that the temperature fluctuation model(5) can in principle explain the origin of this noise. However, according to this model, the power spectrum should depend quadratically on W 1 dR/dT and we observe that SvIV2 oc [W 1 dRldTj'Y with y<1 as it can be seen in 0921-4526/90/$03.50 © 1990 - Elsevier Science Publishers B.V. (North-Holland)