287 research outputs found
Tail States below the Thouless Gap in SNS junctions: Classical Fluctuations
We study the tails of the density of states (DOS) in a diffusive
superconductor-normal metal-superconductor (SNS) junction below the Thouless
gap. We show that long-wave fluctuations of the concentration of impurities in
the normal layer lead to the formation of subgap quasiparticle states, and
calculate the associated subgap DOS in all effective dimensionalities. We
compare the resulting tails with those arising from mesoscopic gap
fluctuations, and determine the dimensionless parameters controlling which
contribution dominates the subgap DOS. We observe that the two contributions
are formally related to each other by a dimensional reduction.Comment: 6 pages, 1 figur
Commensurability effects in Andreev antidot billiards
An Andreev billiard was realized in an array of niobium filled antidots in a
high-mobility InAs/AlGaSb heterostructure. Below the critical temperature T_C
of the Nb dots we observe a strong reduction of the resistance around B=0 and a
suppression of the commensurability peaks, which are usually found in antidot
lattices. Both effects can be explained in a classical Kubo approach by
considering the trajectories of charge carriers in the semiconductor, when
Andreev reflection at the semiconductor-superconductor interface is included.
For perfect Andreev reflection, we expect a complete suppression of the
commensurability features, even though motion at finite B is chaotic.Comment: 4 pages, 4 figure
Andreev Conductance of Chaotic and Integrable Quantum Dots
We examine the voltage V and magnetic field B dependent Andreev conductance
of a chaotic quantum dot coupled via point contacts to a normal metal and a
superconductor. In the case where the contact to the superconductor dominates,
we find that the conductance is consistent with the dot itself behaving as a
superconductor-- it appears as though Andreev reflections are occurring locally
at the interface between the normal lead and the dot. This is contrasted
against the behaviour of an integrable dot, where for a similar strong coupling
to the superconductor, no such effect is seen. The voltage dependence of the
Andreev conductance thus provides an extremely pronounced quantum signature of
the nature of the dot's classical dynamics. For the chaotic dot, we also study
non-monotonic re-entrance effects which occur in both V and B.Comment: 13 pages, 9 figure
Scaling Theory of Conduction Through a Normal-Superconductor Microbridge
The length dependence is computed of the resistance of a disordered
normal-metal wire attached to a superconductor. The scaling of the transmission
eigenvalue distribution with length is obtained exactly in the metallic limit,
by a transformation onto the isobaric flow of a two-dimensional ideal fluid.
The resistance has a minimum for lengths near l/Gamma, with l the mean free
path and Gamma the transmittance of the superconductor interface.Comment: 8 pages, REVTeX-3.0, 3 postscript figures appended as self-extracting
archive, INLO-PUB-94031
Giant Backscattering Peak in Angle-Resolved Andreev Reflection
It is shown analytically and by numerical simulation that the angular
distribution of Andreev reflection by a disordered normal-metal --
superconductor junction has a narrow peak at the angle of incidence. The peak
is higher than the well-known coherent backscattering peak in the normal state,
by a large factor G/G_0 (where G is the conductance of the junction and
G_0=2e^2/h). The enhanced backscattering can be detected by means of ballistic
point contacts.Comment: Instituut-Lorentz, Leiden, The Netherlands, 4 pages, REVTeX-3.0, 3
figure
Mapping (dis)agreement in hydrologic projections
Hydrologic projections are of vital socio-economic importance. However, they are also prone to uncertainty. In order to establish a meaningful range of storylines to support water managers in decision making, we need to reveal the relevant sources of uncertainty. Here, we systematically and extensively investigate uncertainty in hydrologic projections for 605 basins throughout the contiguous US. We show that in the majority of the basins, the sign of change in average annual runoff and discharge timing for the period 2070–2100 compared to 1985–2008 differs among combinations of climate models, hydrologic models, and parameters. Mapping the results revealed that different sources of uncertainty dominate in different regions. Hydrologic model induced uncertainty in the sign of change in mean runoff was related to snow processes and aridity, whereas uncertainty in both mean runoff and discharge timing induced by the climate models was related to disagreement among the models regarding the change in precipitation. Overall, disagreement on the sign of change was more widespread for the mean runoff than for the discharge timing. The results demonstrate the need to define a wide range of quantitative hydrologic storylines, including parameter, hydrologic model, and climate model forcing uncertainty, to support water resource planning
Mesoscopic proximity effect in double barrier Superconductor/Normal Metal junctions
We report transport measurements down to T=60mK of SININ and SNIN structures
in the diffusive limit. We fabricated Al-AlOx/Cu/AlOx/Cu (SININ) and
Al/Cu/AlOx/Cu (SNIN) vertical junctions. For the first time, a zero bias
anomaly was observed in a metallic SININ structure. We attribute this peak of
conductance to coherent multi-reflections of electrons between the two tunnel
barriers. This conductance maximum is quantitatively fitted by the relevant
theory of mesoscopic SININ structures. When the barrier at the SN interface is
removed (SNIN structure), we observe a peak of conductance at finite voltage
accompagnied by an excess of sub-gap conductance.Comment: 4 pages, 4 figures, editorially approved for publication in Phys.
Rev. B Rapid Com
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