8,585 research outputs found
Normal-Superfluid Interface Scattering For Polarized Fermion Gases
We argue that, for the recent experiments with imbalanced fermion gases, a
temperature difference may occur between the normal (N) and the gapped
superfluid (SF) phase. Using the mean-field formalism, we study particle
scattering off the N-SF interface from the deep BCS to the unitary regime. We
show that the thermal conductivity across the interface drops exponentially
fast with increasing , where is the chemical potential imbalance.
This implies a blocking of thermal equilibration between the N and the SF
phase. We also provide a possible mechanism for the creation of gap
oscillations (FFLO-like states) as seen in recent studies on these systems.Comment: 4 pages, 3 figure
Current-phase relation of the SNS junction in a superconducting loop
We study the current-phase relation of the
superconductor/normal/superconductor (SNS) junction imbedded in a
superconducting loop. Considering the current conservation and free energy
minimum conditions, we obtain the persistent currents of the
normal/superconductor (NS) loop. At finite temperature we can explain the
experimentally observed highly non-sinusoidal currents which have maxima near
the zero external flux.Comment: 7 pages, 3 figures, version to appear in Europhys. Let
Andreev reflection at high magnetic fields: Evidence for electron and hole transport in edge states
We have studied magnetotransport in arrays of niobium filled grooves in an
InAs/AlGaSb heterostructure. The critical field of up to 2.6 T permits to enter
the quantum Hall regime. In the superconducting state, we observe strong
magnetoresistance oscillations, whose amplitude exceeds the Shubnikov-de Haas
oscillations by a factor of about two, when normalized to the background.
Additionally, we find that above a geometry-dependent magnetic field value the
sample in the superconducting state has a higher longitudinal resistance than
in the normal state. Both observations can be explained with edge channels
populated with electrons and Andreev reflected holes.Comment: accepted for Phys Rev Lett, some changes to tex
On the effect of combining cooperative communication with sleep mode
Cooperation is crucial in (next-generation) wireless networks as it can greatly attribute to ensuring connectivity, reliability, performance, ... Relaying looks promising in a wide variety of network types (cellular, ad-hoc on-demand), each using a certain protocol. Energy efficiency constitutes another key aspect of such networks, as battery power is often limited, and is typically achieved by sleep mode operation. As the range of applications is very broad, rather than modelling one of the protocols in detail, we construct a high-level model capturing the two essential characteristics of cooperation and energy efficiency: relaying and sleep mode, and study their interaction. The used analytical approach allows for accurate performance evaluation and enables us to unveil less trivial trade-offs and to formulate rules-of-thumb applicable across all potential scenarios
Enhanced Andreev reflection in gapped graphene
We theoretically demonstrate unusual features of superconducting proximity
effect in gapped graphene which presents a pseudospin symmetry-broken
ferromagnet with a net pseudomagnetization. We find that the presence of a band
gap makes the Andreev conductance of graphene superconductor/pseudoferromagnet
(S/PF) junction to behave similar to that of a graphene
ferromagnet-superconductor junction. The energy gap enhance the
pseudospin inverted Andreev conductance of S/PF junction to reach a limiting
maximum value for , which depending on the bias voltage can be
larger than the value for the corresponding junction with no energy gap. We
further demonstrate a damped-oscillatory behavior for the local density of
states of the PF region of S/PF junction and a long-range crossed Andreev
reflection process in PF/S/PF structure with antiparallel alignment of
pseudomagnetizations of PFs, which confirm that, in this respect, the gapped
normal graphene behaves like a ferromagnetic graphene.Comment: 7.2 pages, 5 figures, accepted for publication in Phys. Rev.
Performance of the IEEE 802.16e sleep mode mechanism in the presence of bidirectional traffic
We refine existing performance studies of the WiMAX sleep mode operation to take into account uplink as well as downlink traffic. This as opposed to previous studies which neglected the influence of uplink traffic. We obtain numerically efficient procedures to compute both delay and energy efficiency characteristics. A test scenario with an Individual Subscriber Internet traffic model in both directions shows that even a small amount of uplink traffic has a profound effect on the system performance
Supercurrent transferring through c-axis cuprate Josephson junctions with thick normal-metal-bridge
With simple but exactly solvable model, we investigate the supercurrent
transferring through the c-axis cuprate superconductor-normal
metal-superconductor junctions with the clean normal metal much thicker than
its coherence length. It is shown that the supercurrent as a function of
thickness of the normal metal decreases much slower than the exponential
decaying expected by the proximity effect. The present result may account for
the giant proximity effect observed in the c-axis cuprate SNS junctions.Comment: 6 pages, 4 figure
Conductance Characteristics between a Normal Metal and a Superconductor Carrying a Supercurrent
The low-temperature conductance (G) characteristics between a normal metal
and a clean superconductor (S) carrying a supercurrent parallel to the
interface is theoretically investigated. Increasing causes lowering and
broadening of (1) coherence peaks of s-wave S, and d-wave S at (100) contact,
(2) midgap-states-induced zero-bias conductance peak for d-wave S at (110)
contact, and (3) Andreev-reflection-induced enhancement of within the gap
near the metallic-contact limit. Novel features found include a current-induced
central peak and a three-humped structure at intermediate barrier strength,
etc.Comment: 4 pages, 4 figure
Superconductor-semiconductor magnetic microswitch
A hybrid superconductor--two-dimensional electron gas microdevice is
presented. Its working principle is based on the suppression of Andreev
reflection at the superconductor-semiconductor interface caused by a magnetic
barrier generated by a ferromagnetic strip placed on top of the structure.
Device switching is predicted with fields up to some mT and working frequencies
of several GHz, making it promising for applications ranging from microswitches
and storage cells to magnetic field discriminators.Comment: 4 pages, 3 figures, minor changes to tex
Composite Majorana Fermion Wavefunctions in Nanowires
We consider Majorana fermions (MFs) in quasi-one-dimensional nanowire systems
containing normal and superconducting sections where the topological phase
based on Rashba spin orbit interaction can be tuned by magnetic fields. We
derive explicit analytic solutions of the MF wavefunction in the weak and
strong spin orbit interaction regimes. We find that the wavefunction for one
single MF is a composite object formed by superpositions of different MF
wavefunctions which have nearly disjoint supports in momentum space. These
contributions are coming from the extrema of the spectrum, one centered around
zero momentum and the other around the two Fermi points. As a result, the
various MF wavefunctions have different localization lengths in real space and
interference among them leads to pronounced oscillations of the MF probability
density. For a transparent normal-superconducting junction we find that in the
topological phase the MF leaks out from the superconducting into the normal
section of the wire and is delocalized over the entire normal section, in
agreement with recent numerical results by Chevallier et al. (arXiv:1203.2643)
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