17 research outputs found
The theory of the reentrant effect in susceptibility of cylindrical mesoscopic samples
A theory has been developed to explain the anomalous behavior of the magnetic
susceptibility of a normal metal-superconductor () structure in weak
magnetic fields at millikelvin temperatures. The effect was discovered
experimentally by A.C. Mota et al \cite{10}. In cylindrical superconducting
samples covered with a thin normal pure metal layer, the susceptibility
exhibited a reentrant effect: it started to increase unexpectedly when the
temperature lowered below 100 mK. The effect was observed in mesoscopic
structures when the and metals were in good electric contact. The
theory proposed is essentially based on the properties of the Andreev levels in
the normal metal. When the magnetic field (or temperature) changes, each of the
Andreev levels coincides from time to time with the chemical potential of the
metal. As a result, the state of the structure experiences strong
degeneracy, and the quasiparticle density of states exhibits resonance spikes.
This generates a large paramagnetic contribution to the susceptibility, which
adds up to the diamagnetic contribution thus leading to the reentrant effect.
The explanation proposed was obtained within the model of free electrons. The
theory provides a good description for experimental results [10]
Resonance energy and charge pumping through quantum SINIS contacts
We propose a mechanism of quantum pumping mediated by the spectral flow in a
voltage-biased SINIS quantum junction and realized via the sequential closing
of the minigaps in the energy spectrum in resonance with the Josephson
frequency. We show that the dc current exhibits giant peaks at rational
voltages
Magnetic interference patterns in long disordered Josephson junctions
We study a diffusive superconductor - normal metal - superconductor (SNS)
junction in an external magnetic field. In the limit of a long junction, we
find that the form of the dependence of the Josephson current on the field and
on the length of the junction depends on the ratio between the junction width
and the length associated with the magnetic field. A certain critical ratio
between these two length scales separates two different regimes. In narrow
junctions, the critical current exhibits a pure decay as a function of the
junction length or of the magnetic field. In wide junctions, the critical
current exhibits damped oscillations as a function of the same parameters. This
damped oscillating behavior differs from the Fraunhofer pattern typical for
short or tunnel junctions. In wide and long junctions, superconducting pair
correlations and supercurrent are localized along the edges of the junction.Comment: 9 pages, 4 figures, minor modifications corresponding to the
published versio
Coherent quantum phenomena in mesoscopic metallic conductors (Review Article)
The quantum coherent phenomena in mesoscopic cylindrical metallic conductors have been considered. Pure double-and single-connected normal samples were placed in a longitudinal magnetic field, which generated interference phenomena depending on the magnetic flux through the cross-section of the conductor. The period of the induced oscillations is equal to the flux quantum hc/e of the normal metal. The quantum states are formed in the structures by collisions of the electrons with the dielectric boundary of the sample. The magnetic flux is included in the expression for the spectrum of quasiparticles. The proximity effect and its influence on the modification of the spectrum of quantum coherent phenomena have been investigated. The behavior of cylindrical samples consisting of a superconducting (S) metal with a deposited thin pure normal (N) metal layer has been analyzed. In this structure the electrons are localized in a well bounded by a dielectric on one side and by a superconductor on the other. The specific feature of the generated quantized Andreev levels is that in the varying field H (or temperature T) each of the levels in the well can coincide periodically with the chemical potential of the metal. As a result, the state of the system experiences strong degeneracy and the density of states exhibits resonance spikes of the energy of the NS sample. This makes a significant contribution to the magnetic moment. A theory of the reentrant effect for NS structures has been developed, which interprets the anomalous behavior of the magnetic susceptibility of such structures as a function of the magnetic field and temperatures
Phase-Controlled Force and Magnetization Oscillations in Superconducting Ballistic Nanowires
The emergence of superconductivity-induced phase-controlled forces in the
(0.01-0.1) nN range, and of magnetization oscillations, in nanowire junctions,
is discussed. A giant magnetic response to applied weak magnetic fields, is
predicted in the ballistic Josephson junction formed by a superconducting tip
and a surface, bridged by a normal metal nanowire where Andreev states form.Comment: 5 pages, 3 figure
Andreev reflection and cyclotron motion at superconductor -- normal-metal interfaces
We investigate Andreev reflection at the interface between a superconductor
and a two--dimensional electron system (2DES) in an external magnetic field
such that cyclotron motion is important in the latter. A finite Zeeman
splitting in the 2DES and the presence of diamagnetic screening currents in the
superconductor are incorporated into a microscopic theory of Andreev edge
states, which is based on the Bogoliubov--de Gennes formalism. The
Andreev--reflection contribution to the interface conductance is calculated.
The effect of Zeeman splitting is most visible as a double--step feature in the
conductance through clean interfaces. Due to a screening current, conductance
steps are shifted to larger filling factors and the formation of Andreev edge
states is suppressed below a critical filling factor.Comment: 8 pages, 6 figure
Loss of Andreev Backscattering in Superconducting Quantum Point Contacts
We study effects of magnetic field on the energy spectrum in a
superconducting quantum point contact. The supercurrent induced by the magnetic
field leads to intermode transitions between the electron waves that pass and
do not pass through the constriction. The latter experience normal reflections
which couple the states with opposite momenta inside the quantum channel and
create a minigap in the energy spectrum that depends on the magnetic field
Supercurrents through gated superconductor-normal-metal-superconductor contacts: the Josephson-transistor
We analyze the transport through a narrow ballistic superconductor-normal-
metal-superconductor Josephson contact with non-ideal transmission at the
superconductor-normal-metal interfaces, e.g., due to insulating layers,
effective mass steps, or band misfits (SIN interfaces). The electronic spectrum
in the normal wire is determined through the combination of Andreev- and normal
reflection at the SIN interfaces. Strong normal scattering at the SIN
interfaces introduces electron- and hole-like resonances in the normal region
which show up in the quasi-particle spectrum. These resonances have strong
implications for the critical supercurrent which we find to be determined
by the lowest quasi-particle level: tuning the potential to the
points where electron- and hole-like resonances cross, we find sharp peaks in
, resulting in a transitor effect. We compare the performance of
this Resonant Josephson-Transistor (RJT) with that of a Superconducting Single
Electron Transistor (SSET).Comment: to appear in PRB, 11 pages, 9 figure
Charge and Spin Effects in Mesoscopic Josephson Junctions
We consider the charge and spin effects in low dimensional superconducting
weak links. The first part of the review deals with the effects of
electron-electron interaction in Superconductor/Luttinger liquid/Superconductor
junctions. The experimental realization of this mesoscopic hybrid system can be
the individual single wall carbon nanotube that bridges the gap between two
bulk superconductors. The dc Josephson current through a Luttinger liquid in
the limits of perfectly and poorly transmitting junctions is evaluated. The
relationship between the Josephson effect in a long SNS junction and the
Casimir effect is discussed. In the second part of the paper we review the
recent results concerning the influence of the Zeeman and Rashba interactions
on the thermodynamical properties of ballistic S/QW/S junction fabricated in
two dimensional electron gas. It is shown that in magnetically controlled
junction there are conditions for resonant Cooper pair transition which results
in giant supercurrent through a tunnel junction and a giant magnetic response
of a multichannel SNS junction. The supercurrent induced by the joint action of
the Zeeman and Rashba interactions in 1D quantum wires connected to bulk
superconductors is predicted.Comment: 36 pages, 8 figures; minor changes in reference
The role of the self-consistent equation in identifying the Andreev spectrum in a mesoscopic NS structure
Adifferential self-consistent equation has been obtained for a dimensionless magnetic flux in a NS structure, which is responsible for the magnetic moment jumps in the system.A differential self-consistent equation has been obtained for a dimensionless magnetic flux in a NS structure, which is responsible for the magnetic moment jumps in the system