Observation of distinct, temperature dependent flux noise near bicrystal grain boundaries in YBa2Cu3O7-x films

The characteristics of the magnetic flux noise in high temperature supercon ducting thin-films of yttrium-barium-copper-oxide (YBa2Cu3O7) in the vicini ty of artificial grain boundaries have been studied by means of a low criti cal temperature superconducting quantum interference device (SQUID) magneto meter. The measured power spectrum of the flux noise typically shows 1/f-be haviour at low frequencies. This is, in particular, evident near the transi tion temperature. When measuring the flux noise near an artificial grain bo undary we observe in selected samples additional Lorentzian type spectra in narrow temperature ranges indicative for well-defined barriers for flux ho pping. Such spectra are not observed when measuring away from the grain bou ndary. The distinct fluctuators are seen in the 60-80 K interval correspond ing to barrier heights of order 0.1-0.4 eV. If present in Josephson junctio ns patterned across such artificial grain boundaries, they could lead to se rious limitations in the junction performance in certain temperature ranges . (C) 2000 Elsevier Science B.V. All rights reserved.