Distribution of flux pinning energies in YBa sub 2 Cu sub 3 O sub 7 sub - sub / delta / and Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8 sub + sub / delta / from flux noise

The spectral density of magnetic flux noise measured in high-temp. superconductors in low magnetic fields scales approx as the inverse of frequency and increases with temp. The temp. and frequency dependence of noise are used to determine the pinning energies of individual flux vortices in thermal equilibrium. The distribution of pinning energies below 0.1 eV in YBa sub 2 Cu sub 3 O sub 7 sub - sub / delta / and near 0.2 eV in Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8 sub + sub / delta / are determined. Noise power is proportional to the ambient magnetic field, indicating that vortex motion is uncorrelated.