Size effect of 1/f noise in the normal state of YBa2Cu3O7-δ

The 1/f noise power spectral density in the normal state of two series of YBa2Cu3O7-delta samples-microbridges of width 4-200 mu m and ultrathin films of thickness 2.4-10.8 nm-are measured at temperatures from 80 to 300 K. Two characteristic lengths-one in the ab plane with a magnitude of about 10(1) mu m and another along the c axis with a magnitude of about 10(0) nm - are discovered. The noise level decreases sharply below the characteristic lengths. Th lowest noise level observed is in the range of that of normal metals. The experimental data can be described reasonably well by the Dutta-Horn thermally activated model. Some possible mechanisms are also discussed.