Random Magnetic Flux Research Articles

Electron hopping in the presence of random flux.

We calculate the distribution of single-particle states for a spinless electron hopping on a two-dimensional square lattice in the presence of random magnetic flux. The flux is taken to be uniformly random between 0 and 1 flux quantum, taking on either continuous or rational values. We consider nearest-neighbor and next-nearest-neighbor hopping. Compared with the density of states without flux, the allowed energies span a smaller range, and the distribution is relatively flat. If states are filled with noninteracting fermions, the random flux lowers the energy for a wide range of filling fractions and next-nearest-neighbor couplings. Examination of the wave functions shows that most of the states are extended with a tail of localized states near the band edge.

Operating characteristics of thin-film rf-biased SQUID’s

Operating characteristics of rf-biased thin-film SQUID’s of diameter as large as 1 cm are reported. Observation on these SQUID’s have experimentally verified several of their conventionally assumed properties such as the dependence of the quantum interference signal on critical current of the weak link, total inductance of the SQUID, inductive coupling between drive coil and the SQUID, and random magnetic flux noise. A simple technique of lowering the inductance, and hence increasing the signal, of large-diameter SQUID’s is reported.