A study of 1/f noise in the normal state of high-Tc superconductors

Abstract

1/f noise measurements were done on two classes of materials, Tl2Ba2Ca(n-1)CunO(4+2n) (n=2,3) and Y1Ba2Cu3Ox, that exhibit superconductivity above 77K. In Tl2Ba2Ca(n-1)CunO(4+2n) materials, 1/f noise was measured on thin films and bulk samples. The measurements on the bulk samples of these materials are the first reported. The obtained experimental results on these samples indicate that 1/f noise is not an intrinsic property of high-Tc superconductors. Two important facts were discovered. First, a very low noise level was observed in the thin film samples and second, in the superconducting transition region, no enhanced noise was observed for some samples. Both these results, which are important from both physics and engineering point of views, are reported for the first time. In Y1Ba2Cu3Ox material, measurements of 1/f noise were done on single crystals in order to obtain more fundamental results. The measurements on the single crystals are the first reported. The measurements were performed in two crystallographic directions, ab-planes and coaxes, of the crystals. Noise level and its temperature dependence were found to be similar in both the directions, in spite of a very different resistivity behavior, in the normal state of the material. In the superconducting transition region, anisotropic behavior of 1/f noise was observed. The noise was found to be enhanced by several orders of magnitude along the c-axis of the crystal and no such enhancement of noise was observed in the ab-plane of the crystal. The anisotropic behavior of 1/f noise is the first reported. Possible explanations for the observed anisotropic behavior of noise are discussed along with various models. The plausible sources of 1/f noise in these materials are then argued to be related to tunneling conduction mechanism and thermally activated vortex motion.