Magnetoconductance fluctuations in mesoscopic spin glasses

Results of numerical studies of conductance of a two-dimensional tight-binding system with random potentials and coupled to a three-dimensional Ising spin glass are presented. The dynamics of the systems are determined by the Monte Carlo process of the Ising spins. The paper is focused on the effects of the magnetic field which couples to the lattice spins and changes their configuration. The conductance noise in the presence of the field is given by a power law, like in the absence of the field. The magnetoconductance fluctuations, obtained from studying time-averaged trains of conductance for a given field, increase in amplitude on lowering temperature. This is unlike what happens with the thermal noise and with what happens with magnetoconductance fluctuations in spin ferromagnets. The dependence of conductance on the magnetic field depends on the size of the field increments and on the starting spin configuration. It depends also, to a lesser degree, on the time interval used in averaging. The field-cycling magnetoconductance curves are not reproducible. Experimental results, on the other hand, are, to a large extent, reproducible. Possible reasons for this discrepancy are discussed.