Abstract: The local modification of an insulating GdBa2Cu3O6.5 thin film, made superconducting by illumination with a near-field scanning optical microscope (NSOM), is reported. A 100-nm aperture NSOM probe acts as a sub- wavelength light source of wavelength ?(exc)=480-650 nm, locally generating photocarriers in an otherwise insulating GdBa2-Cu3O6.5 thin film. Of the photogenerated electron-hole pairs, electrons are trapped in the crystallographic lattice, defining an electrostatic confining potential to enable the holes to move. Reflectance measurements at ? = 1.55 ?m at room temperature show that photocarriers can be induced and constrained to move on a ?? 200 nm scale for all investigated ?(exc). Photogenerated wires present a superconducting critical temperature T(c) = 12 K with a critical current density J(c) = 104 A cm-2. Exploiting the flexibility provided by photodoping through a NSOM probe, a junction was written by photodoping a wire with a narrow (? 50 nm) under-illuminated gap. The strong magnetic field modulation of the critical current provides a clear signature of the existence of a Josephson effect in the junction.

Abstract: We present results on the Hall coefficient RH in the normal state for a GdBa2Cu3O7-?/La0.75 Sr0.25MnO3 bilayer and a La0.75Sr0.25MnO3 film grown by dc magnetron sputtering on (1 0 0) SrTiO3. We find that the electric transport on the bilayer can be qualitatively described using a simple parallel layers model. The GdBa2Cu3O7-? layer presents a carrier density approximately equal to that reported for 7 – ? = 6.85 oxygen doping. Also we observe an unexpected presence of two Hall resistivity regimes, effects that may be associated with the internal magnetic field induced on the superconducting layer by the ferromagnetic layer.

Abstract: Molybdenum oxynitride (MoNxOy) thin films were grown by reactive sputtering on Si (100) substrates at room temperature. The partial pressure of Ar was fixed at 90%, and the remaining 10% was adjusted with mixtures N2:O2 (varying from pure N2 to pure O2). The electrical properties of the films depend on the chemical composition. Thin films grown using mixtures up to 2% O2 have γ-Mo2N phase and display superconductivity. The superconducting critical temperature Tc reduces from ∼6.8 K to below 3.0 K as the oxygen increases. On the other hand, the films are mostly amorphous for gas mixtures above 2% O2. The electrical conductivity shows a semiconductor-like behavior well described by variable-range hopping conduction. The analysis of the optical properties reveals that the samples do not have a defined semiconductor bandgap, indicating that the high structural disorder produces electron excitation for a wide range of energies.

Abstract: The illumination of PryGd1-yBa2Cu 3Ox semiconducting and superconducting thin films increases their critical temperatures and decreases their normal state resistivities if and only if the films are oxygen deficient. Moreover, these changes are enhanced near the Pr-induced metal-insulator transition. Light also causes a contraction of the c-axis in YBa2Cu3Ox which is correlated with the observed photoinduced resistivity changes. These changes are similar to those observed when oxygen-deficient YBa 2Cu3Ox is enriched with oxygen or annealed at room temperature after quenching from high temperatures.