82 research outputs found
Influence of impurity-scattering on tunneling conductance in d-wave superconductors with broken time reversal symmetry
Effects of impurity scattering on tunneling conductance in dirty
normal-metal/insulator/superconductor junctions are studied based on the Kubo
formula and the recursive Green function method. The zero-bias conductance peak
(ZBCP) is a consequence of the unconventional pairing symmetry in
superconductors. The impurity scattering in normal metals suppresses the
amplitude of the ZBCP. The degree of the suppression agrees well with results
of the quasiclassical Green function theory. When superconductors have
+is-wave pairing symmetry, the time-reversal symmetry is broken in
superconductors and the ZBCP splits into two peaks. The random impurity
scattering reduces the height of the two splitting peaks. The position of the
splitting peaks, however, almost remains unchanged even in the presence of the
strong impurity scattering. Thus the two splitting peaks never merge into a
single ZBCP.Comment: 12 pages, 5 figures, using jpsj2.cls and overcite.st
A phenomenological theory of zero-energy Andreev resonant states
A conceptual consideration is given to a zero-energy state (ZES) at the
surface of unconventional superconductors. The reflection coefficients in
normal-metal / superconductor (NS) junctions are calculated based on a
phenomenological description of the reflection processes of a quasiparticle.
The phenomenological theory reveals the importance of the sign change in the
pair potential for the formation of the ZES. The ZES is observed as the
zero-bias conductance peak (ZBCP) in the differential conductance of NS
junctions. The split of the ZBCP due to broken time-reversal symmetry states is
naturally understood in the present theory. We also discuss effects of external
magnetic fields on the ZBCP.Comment: 12 page
Theory of charge transport in diffusive normal metal / unconventional singlet superconductor contacts
We analyze the transport properties of contacts between unconventional
superconductor and normal diffusive metal in the framework of the extended
circuit theory. We obtain a general boundary condition for the Keldysh-Nambu
Green's functions at the interface that is valid for arbitrary transparencies
of the interface. This allows us to investigate the voltage-dependent
conductance (conductance spectrum) of a diffusive normal metal (DN)/
unconventional singlet superconductor junction in both ballistic and diffusive
cases. For d-wave superconductor, we calculate conductance spectra numerically
for different orientations of the junctions, resistances, Thouless energies in
DN, and transparencies of the interface. We demonstrate that conductance
spectra exhibit a variety of features including a -shaped gap-like
structure, zero bias conductance peak (ZBCP) and zero bias conductance dip
(ZBCD). We show that two distinct mechanisms: (i) coherent Andreev reflection
(CAR) in DN and (ii) formation of midgap Andreev bound state (MABS) at the
interface of d-wave superconductors, are responsible for ZBCP, their relative
importance being dependent on the angle between the interface normal
and the crystal axis of d-wave superconductors. For , the ZBCP is due
to CAR in the junctions of low transparency with small Thouless energies, this
is similar to the case of diffusive normal metal / insulator /s-wave
superconductor junctions. With increase of from zero to , the
MABS contribution to ZBCP becomes more prominent and the effect of CAR is
gradually suppressed. Such complex spectral features shall be observable in
conductance spectra of realistic high- junctions at very low temperature
Tunneling Spectra of Skutterudite PrOs_4Sb_{12}
The tunnel conductance in normal-metal / insulator / PrOsSb
junctions is theoretically studied, where skutterudite PrOsSb is
considered to be an unconventional superconductor. The conductance are
calculated for several pair potentials which have been proposed in recent
works. The results show that the conductance is sensitive to the relation
between the direction of electric currents and the position of point nodes. We
also show that the conductance spectra often deviate from the shape of the bulk
density of states and that the sub gap spectra have peak structures in the case
of the spin-triplet pair potentials. The results indicate that the tunnel
conductance is a useful tool to obtain an information of the pairing symmetry.Comment: 9 page
Water and Sediment Discharges from a Glacier-covered Basin under Maritime Climate in Kamchatka Peninsula, Russia
In order to clarify the characteristics of water and sediment discharges from glacier-covered basins under maritime climate, hydrological observations were carried out within a drainage basin which contains Koryto Glacier in Kamchatka Peninsula, Russia. Water discharge of a proglacial stream near the glacier terminus varied between 3 and 12 m^3 s^[-1] during the summer of 2000. Variation in suspended sediment concentration was positively correlated with water discharge, and values of sediment concentration ranged from 1.0 to 0.1 g1^[-1]. A runoff model which consists of two linear reservoirs in series was applied to the basin for simulating discharge variation. Considering a seasonal change in glacier drainage systems, this model can simulate stream discharge well. Three different models based on rating curve, multiple regression and sediment storage for suspended sediment transport estimation yield the total suspended sediment load during the observation period to be 10 × 10^6 kg. The sediment storage model assuming a reservoir beneath the glacier could bring the best estimate of variation in suspended sediment load. However, the multiple regression model gives a reasonable result and is also applicable for prediction.International Symposium on "Dawn of a New Natural History - Integration of Geoscience and Biodiversity Studies". 5-6 March 2004. Sapporo, Japan
Surface Heat Balance and Spatially Distributed Ablation Modelling at Koryto Glacier, Kamchatka Peninsula, Russia
To investigate the characteristics of ablation at Koryto Glacier, a mountain glacier under maritime climate in Kamchatka Peninsula, Russia, we made field observations from August to early September 2000. At a site near the equilibrium line, the 31-day average net radiation, sensible heat flux, and latent heat flux were 43, 59 and 31 W-2, respectively. We developed a new distributed ablation model, which only needs measurements of air temperature and global radiation at one site. Hourly ablation rates at this site obtained by the energy balance method are related to measured air temperature and global radiation by linear multiple regression. A different set of multiple regression coefficients is fitted for snow and ice surfaces. Better estimates of ablation rate can be obtained by this approach than by other temperature index models. These equations are then applied to each grid cell of a digital elevation model to estimate spatially distributed hourly melt. Air temperature is extrapolated using a constant temperature lapse rate and global radiation is distributed considering topographic effects. The model enables us to calculate the hourly spatial distribution of ablation rates within the glacier area and could well provide a realistic simulation of ablation over the whole glacier
Influence of weather conditions and spatial variability on glacier surface melt in Chilean Patagonia
Influence of weather conditions and spatial variability on glacier surface melt in Chilean Patagonia
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