Ju Gao

Preparation of ramp-type Josephson junctions using an Nd2CuO4 barrier

Ramp-type Josephson junctions with a Nd2CuO4 (NCO) barrier have been fabricated on (001)-SrTiO3 using RF magnetron sputtering. Such an NCO barrier has a highly stable T-214 structure and is chemically compatible with the 123-superconductors. The lattice constant and thermal expansion coefficient of YBa2Cu3Oy and NCO being very similar ensures a high transparency at the superconductor/barrier interface, thus significantly increasing the reproducibility. Its resistivity is also remarkably higher than that of many currently used barrier materials. These junctions showed a typical resistively shunted junction-like current–voltage characterization and Shapiro steps under irradiation using a microwave field. The current uniformity of these junctions has also been enhanced significantly. The temperature dependence of the junction parameters and the scaling behaviour are discussed and compared with other high temperature Josephson junctions.

Anomalous Resistance Behavior Observed Across the Interface of Superconducting YBa2Cu3O7 and Ferromagnetic La0.7Ca0.3MnO3

Abstract Temperature dependencies of the resistance across the interface of superconducting YBa2Cu3O7 and ferromagnetic La0.7Ca0.3MnO3 were investigated in La0.7Ca0.3MnO3/YBa2Cu3O7 double-layer and cross-strip samples. Anomalous resistance behavior, a relatively large resistance value with a superconducting-like transition, was observed in both samples. In the cross-strip sample the voltage signal changed to extremely large negative values in the temperature region of 170–90xa0K, which was corresponding to the resistance peak in the LCMO strip. A possible explanation is discussed.

Excess Current in High-Tc Josephson Junction with Thin PrBa2Cu3Oy Barrier Layer

Abstract The temperature dependence of excess current in the ramp-edge YBa 2 Cu 3 O y /PrBa 2 Cu 3 O y /YBa 2 Cu 3 O y Josephson junctions has been studied. The experimental results indicated that excess current may be caused by Andreev reflection at the SN interfaces of SNS junctions. It was found that the temperature dependence of excess current is the same as that of order parameter at the N side of SN interface. This is in agreement with the prediction of theory. The amplitude of the excess current is the same order as that of critical current.

Large low-field magnetoresistance observed in heterostructure multilayers

The behaviour of resistivity versus temperature in a series of (LCMO)/(GCMO) multilayers has been studied. The resistivity peak temperature of the multilayers decreases with decreasing thickness of the LCMO layers. Large low-field magnetoresistance (LFMR) of % is obtained at 78.5 K in heterostructure LCMO/GCMO multilayers when a magnetic field is swept within Oe. This result suggests that the interface strain between LCMO and GCMO layers may influence the magnetic transport properties and a suitable film structure could be used to increase the LFMR.

Threshold stress of 90° domain switching in the misfit strain–external stress phase diagram

The nanoscale polydomain switchings within valid single grains of Pb(Zr0.52Ti0.48)O3 ferroelectric thin film were observed by piezoresponse force microscopy under the different loading forces. According to the switching process, the ac/aa*(ac−/aa* and ac+/aa*) and c/ac/aa*(c−/ac+/aa*) polydomain states were specially introduced to describe the force-induced polydomain switchings at the simplification of uniform stress distribution. The misfit strain–external stress phase diagrams and the external stress–polarization components curves were simulated in order to explain two different kinds of polydomain states transition within the selected grains. From the phase diagrams, the threshold mechanical stresses at the misfit strain 0.001 evaluated by X-ray diffraction were −1.24 GPa for the phase transition from c−/ac+/aa* to aa* phase and −1.20 GPa from ac+/aa* to aa* phase. The conclusions were corresponding to the threshold mechanical stress of domain switchings obtained from the experimental results.

Giant photosensitivity of a-C:Co/GaAs/Ag p-n-metal junctions

The Schottky contact behavior of Silver (Ag) with parts of semiconductor materials, such as GaAs and GaN, greatly limits its application for electrodes in electronic devices. Here, a giant photosensitivity is observed in Co-doped amorphous carbon (a-C:Co) films deposited on n-type low-resistance GaAs substrates through a Schottky contact between GaAs and Ag. We ascribe the giant photosensitivity to the turn-on voltage difference in the series-opposing connected a-C:Co/GaAs photosensitive diode and GaAs/Ag Schottky junction with and without light illumination, and also to the surface plasmon resonance absorption of Co nanoparticles.

The contact and photoconductivity characteristics between Co doped amorphous carbon and GaAs: n-type low-resistivity and semi-insulated high-resistivity GaAs

The Co doped amorphous carbon films (a-C:Co), deposited by pulsed laser deposition, show p-n and ohmic contact characteristics with n-type low resistivity GaAs (L-GaAs) and semi-insulated high-resistivity GaAs (S-GaAs). The photosensitivity enhances for a-C:Co/L-GaAs, while inverse decreases for a-C:Co/S-GaAs heterojunction, respectively. Furthermore, the enhanced photosensitivity for the a-C:Co/L-GaAs/Ag heterojunction also shows deposition temperature dependence behavior, and the optimum deposition temperature is around 500 °C.

Current-Induced Reversible Resistance Jumps in La

Two spatially confined La0.8Ca0.2MnO3 (LCMO) microbridges with different widths, starting from a single LCMO film (3 mm×5 mm), are fabricated by optical lithography. A second new and robust metal-insulator transition (MIT) peak at about 75 K appears, in addition to the normal MIT at 180 K observed in the standard LCMO film. When the two bridges are processed by currents of high densities, interesting reversible resistance jumps are excited only around the new peak. A stronger dependence of resistance jump on current excitation is found for the bridge with a smaller width. The temperature driven transition between new excited multiple metastable states are involved to explain the interesting low-temperature ultra-sharp jumps.