2,288 research outputs found
Theory of Josephson effect in chiral p-wave superconductor / diffusive normal metal / chiral p-wave superconductor junctions
We study the Josephson effect between chiral p-wave superconductor /
diffusive normal metal (DN) / chiral p-wave superconductor (CP/DN/CP) junctions
using quasiclassical Green's function formalism with proper boundary
conditions. The px+ipy-wave symmetry of superconducting order parameter is
chosen which is believed to be a pairing state in Sr2RuO4. It is shown that the
Cooper pairs induced in DN have an odd-frequency spin-triplet s-wave symmetry,
where pair amplitude is an odd function of Matsubara frequency. Despite the
peculiar symmetry properties of the Cooper pairs, the behavior of the Josephson
current is rather conventional. We have found that the current phase relation
is almost sinusoidal and the Josephson current is proportional to exp(-L/xi),
where xi is the coherence length of the Cooper pair in DN and L is the length
of DN. The Josephson current between CP / diffusive ferromagnet metal (DF) / CP
junctions is also calculated. It is shown that the 0-pi transition can be
realized by varying temperature or junction length L similar to the case of
conventional s-wave junctions. These results may serve as a guide to study
superconducting state of Sr2RuO4.Comment: 9 pages, 9 figure
Multivalued memory effects in electronic phase-change manganites controlled by Joule heating
Non-volatile multivalued memory effects caused by magnetic fields, currents,
and voltage pulses are studied in Nd_{0.65}Ca_{0.35}MnO_3 and
(Nd_{1-y}Sm_{y})_{0.5}Sr_{0.5}MnO_3 (y=0.75) single crystals in the hysteretic
region between ferromagnetic metallic and charge-ordered insulating states. The
current/voltage effects observed in this study are explained by the
self-heating effect, which enable us to control the colossal electroresistance
effects. This thermal-cycle induced switching between electronic solid and
liquid states can be regarded as electronic version of atomic crystal/amorphous
transitions in phase-change chalcogenides.Comment: 5 pages, 4 figures. to appear in Phys. Rev.
Hysteretic current-voltage characteristics and resistance switching at an epitaxial oxide Schottky junction SrRuO/SrTiNbO
Transport properties have been studied for a perovskite heterojunction
consisting of SrRuO (SRO) film epitaxially grown on
SrTiNbO (Nb:STO) substrate. The SRO/Nb:STO interface
exhibits rectifying current-voltage (-) characteristics agreeing with
those of a Schottky junction composed of a deep work-function metal (SRO) and
an -type semiconductor (Nb:STO). A hysteresis appears in the -
characteristics, where high resistance and low resistance states are induced by
reverse and forward bias stresses, respectively. The resistance switching is
also triggered by applying short voltage pulses of 1 s - 10 ms duration.Comment: 3 pages, 3 figures, Appl. Phys. Lett., in pres
Angular dependence of Josephson currents in unconventional superconducting junctions
Josephson effect in junctions between unconventional superconductors is
studied theoretically within the model describing the effects of interface
roughness. The particularly important issue of applicability of the frequently
used Sigrist-Rice formula for Josephson current in d-wave superconductor /
insulator / d-wave superconductor junctions is addressed. We show that although
the SR formula is not applicable in the ballistic case, it works well for rough
interfaces when the diffusive normal metal regions exist between the d-wave
superconductor and the insulator. It is shown that the SR approach only takes
into account the component of the d-wave pair potential symmetric with respect
to an inversion around the plane perpendicular to the interface. Similar
formula can be derived for general unconventional superconductors with
arbitrary angular momentum l.Comment: 4 pages, 4 figure
Resistive switching effects on the spatial distribution of phases in metal-complex oxide interfaces
In order to determine the key parameters that control the resistive switching
mechanism in metal-complex oxides interfaces, we have studied the electrical
properties of metal / YBa2Cu3O7-d (YBCO) interfaces using metals with different
oxidation energy and work function (Au, Pt, Ag) deposited by sputtering on the
surface of a YBCO ceramic sample. By analyzing the IV characteristics of the
contact interfaces and the temperature dependence of their resistance, we
inferred that ion migration may generate or cancel conducting filaments, which
modify the resistance near the interface, in accordance with the predictions of
a recent model.Comment: 3 pages, 5 figures, to be published in Physica B. Corresponding
author: C. Acha ([email protected]
Multi-Temporal Remote Sensing of Landuse Dynamics in Zaria, Nigeria
This study assesses the impact of growth of Zaria town on the changing pattern of the different landuse/land cover types within and around the town, using Remote Sensing and GIS techniques. Zaria is witnessing rapid rate of urbanization as a consequence of the establishment of the Ahmadu Bello University at Zaria in 1962. It is one of the fastest growing settlements in northern Nigeria. The increasing population from the University community has led to serious competition for land among different landuse types. Multi-temporal satellite imageries for three and half decades (1973, 1990, 1999 and 2006) were used to assess the impact of the growth of Zaria town on the changing pattern of the different landuse/land cover (LULC) types using Remote Sensing GIS techniques. The images were transformed, enhanced, sampled and re-sampled, classified and crossed for change detection. Results of the analysis showed that although there are year to year variations in area under each landuse type, net change detection showed that built up area has been on the increase each year encroaching on scrubland, farmlands and fadama to shrink. Keywords: change detection, image crossing, multi-temporal, multi-spectral
Imaging Oxygen Defects and their Motion at a Manganite Surface
Manganites are technologically important materials, used widely as solid
oxide fuel cell cathodes: they have also been shown to exhibit
electroresistance. Oxygen bulk diffusion and surface exchange processes are
critical for catalytic action, and numerous studies of manganites have linked
electroresistance to electrochemical oxygen migration. Direct imaging of
individual oxygen defects is needed to underpin understanding of these
important processes. It is not currently possible to collect the required
images in the bulk, but scanning tunnelling microscopy could provide such data
for surfaces. Here we show the first atomic resolution images of oxygen defects
at a manganite surface. Our experiments also reveal defect dynamics, including
oxygen adatom migration, vacancy-adatom recombination and adatom bistability.
Beyond providing an experimental basis for testing models describing the
microscopics of oxygen migration at transition metal oxide interfaces, our work
resolves the long-standing puzzle of why scanning tunnelling microscopy is more
challenging for layered manganites than for cuprates.Comment: 7 figure
Andreev bound states and tunneling characteristics of a non-centrosymmetric superconductor
The tunneling characteristics of planar junctions between a normal metal and
a non-centrosymmetric superconductor like CePt3Si are examined. It is shown
that the superconducting phase with mixed parity can give rise to
characteristic zero-bias anomalies in certain junction directions. The origin
of these zero-bias anomalies are Andreev bound states at the interface. The
tunneling characteristics for different directions allow to test the structure
of the parity-mixed pairing state.Comment: 4 pages, 3 figure
- …