Noise measurement near the transition region inYBa2Cu3

Abstract

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.

Current noise in high Tc granular superconductors under non-stationary conditions of current and magnetic field

“…In a different situation, when weak links do not play an important role, the noise may be predominantly generated by fluxoids motion. [4,5,16,17,18]. It is interesting to notice that series of random steps having the same sign when the resistance of the specimen increases or decreases gives rise in general to a 1/f 2 component, while random steps of random signs may give rise to a 1/f spectrum under suitable conditions for their distribution.…”

“…As observed experimentally, there is a strong difference in the noises generated in stationary and non stationary conditions. When a constant current is flowing in a HTSC made resistive by a d.c. magnetic field (or by the current itself when it is sufficiently large) a current noise is generated whose power spectrum is of the 1/f type [2,3,4,5,6], while when the current or the field are changing an additional noise component occurs whose power spectrum is of the 1/f 2 type [7]. This component dominates the low frequency part of the power spectrum, and, in the case of the magnetic field variation, it is so large that the 1/f component is negligible and the whole spectrum appears to be of the 1/f 2 type.…”

Origin of 1/f noise peaks of YBa{sub 2}Cu{sub 3}O{sub x} films in a magnetic field

“…Generally, Xa moving flux bundle is pinned after moving a distance I, the phase change due to the motion is no longer a multiple of 2x, but should be reduced by a factor of UL where L is the width of the strip [16]. If a flux bundle moves with a velocity v = UT, then V AY=CD- (2). L To obtain a full noise spectrum, we have to average over all possible individual spectra (subpulses) with an appropriate distribution function.…”

“…Number of models has been suggested to explain the origins of llfnoise near Tc. Extremely large noise observed in the bulk samples of YBa2Cu3OX was explained as the noisy hopping processes across the inhomogeneous boundaries [ 11. For polycrystalline thin films of YBa2Cu3OX, Lee et al [2] observed two noise peaks, one near the onset Tc and the other near the zero-resistance temperature. The noise peaks near the onset was magnetic field independent and well fitted to a thermal fluctuation effect, while the magnitude of the peak near the zero-resistance temperature decreased as applied field increased up to 50 gauss.…”

1/f Noise in the superconducting transition of a MgB2 thin film

“…Many reports in the literature have shown that in high-T c superconducting granular ceramic thin films, e.g. YBCO, that the excess noise approaches zero in the superconducting state and that it rises sharply in the transition region with a 1/f a type spectrum with a 6 1 over a wide range of frequencies [2]. Gandini et al [3] have reported similar findings for a granular MgB 2 thin film sample, they postulate a percolation process between grains in the film for the origin of the noise and show 1/f a noise dependence with a % 1.5 in the range 1-100 Hz.…”