Observation of a nonmagnetic hard gap in amorphous In/InOx films in the hopping regime

Magnetic hard gap due to bound magnetic polarons in the localized regime

We investigate the low temperature electron transport properties of manganese doped lead sulfide films. The system shows variable range hopping at low temperatures that crosses over into an activation regime at even lower temperatures. This crossover is destroyed by an applied magnetic field which suggests a magnetic origin of the hard gap, associated with bound magnetic polarons. Even though the gap forms around the superconducting transition temperature of lead, we do not find evidence of this being due to insulator-superconductor transition. Comparison with undoped PbS films, which do not show the activated transport behavior, suggests that bound magnetic polarons create the hard gap in the system that can be closed by magnetic fields.

Role of percolation in the conductance of electrolyte-gated SrTiO3

We study the electrolyte-gate-induced conductance at the surface of SrTiO(3)(001). We find two distinct transport regimes as a function of gate voltage. At high carrier densities, a percolative metallic state is induced in which, at low temperatures, clear signatures of a Kondo effect are observed. At lower carrier densities, the resistance diverges at low temperatures and can be well described by a 2D variable range hopping model. We postulate that this derives from nonpercolative transport due to inhomogeneous electric fields from imperfectly ordered ions at the electrolyte-oxide interface.

Tunneling magnetoresistance with sign inversion in junctions based on iron oxide nanocrystal superlattices

Magnetic tunnel junctions sandwiching a superlattice thin film of iron oxide nanocrystals (NCs) have been investigated. The transport was found to be controlled by Coulomb blockade and single-electron tunneling, already at room temperature. A good correlation was identified to hold between the tunnel magnetoresistance (TMR), the expected magnetic properties of the NC arrays, the charging energies evaluated from current-voltage curves, and the temperature dependence of the junction resistance. Notably, for the first time, a switching from negative to positive TMR was observed across the Verwey transition, with a strong enhancement of TMR at low temperatures.

Spin-dependent variable range hopping and magnetoresistance in Ti(1-x)Co(x)O(2) and Zn(1-x)Co(x)O magnetic semiconductor films

Magnetic transport properties in Ti(1-x)Co(x)O(2) and Zn(1-x)Co(x)O magnetic semiconductors have been studied experimentally and theoretically. A linear relation of lnρ versus T(-1/2) (ρ is sheet resistance and T is temperature), which shows different slopes and intersections at different magnetic fields, was observed experimentally in the low temperature range. The spin-dependent variable range hopping model has been proposed by taking into account the electron-electron Coulomb interaction and the spin-spin exchange interaction in the same frame, which can well describe the observed magnetic transport properties in Ti(1-x)Co(x)O(2) and Zn(1-x)Co(x)O magnetic semiconductors.