Coulomb Gap and Correlated Vortex Pinning in Superconductors

The positions of columnar pins and magnetic flux lines determined from a decoration experiment on Bi₂Sr₂CaCu₂{O}₈$ were used to calculate the distribution of pinning energies in the Bose glass phase. A wide Coulomb gap is found, with effective gap exponent ${s}eff{≈}1.2$, as a result of interactions between the vortices. As a consequence, the variable-range hopping transport of flux lines is considerably reduced with respect to the noninteracting case, the effective Mott exponent being enhanced from p₀0ex0ex=0ex0ex1/3 to peff≈0.5 for this sample.