Noise Properties of YBCO Nanostructures

Voltage noise measurements on close to optimally doped YBa2Cu3O7-δ nanostructures have been performed. The measured resistance noise at temperature T = 96 K (above critical temperature TC = 85 K) shows a quadratic dependence on the bias current, e.g., the voltage power spectral density SV α V 2. Moreover, the normalized voltage noise SV V2 is inversely proportional to the device volume. This is a clear indication that the noise is the result of an ensemble of independent resistive fluctuators, evenly distributed within the sample volume. For our structures, we obtain a product SVV2 × Vol. = const. ≈ 6 × 10-33 m3/Hz resulting in a Hooge's parameter 3.4 × 10-4, which is among the lowest reported in literature. At lower temperature, T = 2 K (well below TC) the total voltage fluctuations are given by the combined effect of critical current fluctuations and resistance fluctuations. For the critical current noise, we obtain a product SI/IC2 × Vol. = const. ≈ 6 × 10-32 m3/Hz. The larger value of the relative critical current noise is most probably due to the fact that the critical current is determined by edge effects whereas the resistance is given by the total volume of the device.