Investigation on origin of excess noise in superconducting and normal state BiSrCaCuO films

Noise power spectral density was measured on superconducting and normal state BiSrCaCuO films with variation of temperature, frequency, applied current and external magnetic field. A noise peak was found below superconducting transition temperature. Noise peaks in the superconducting films decreased with an increase of external magnetic field, and had a maximum at a certain applied current. The origin of the excess noise was analysed using a thermal fluctuation model and a vortex motion model. The conclusion was that the noise was associated with vortex motion and film quality. Large 1f noise in normal state BiSrCaCuO films was estimated, and it was several orders of magnitude greater than noise in normal metals, suggesting a different noise mechanism.