pinecone/core-2020-05-10-deduplication huggingface dataset:
Long-range coherence and mesoscopic transport in N-S metallic structures

We review the mesoscopic transport in a diffusive proximity superconductor
made of a normal metal (N) in metallic contact with a superconductor (S). The
Andreev reflection of electrons on the N-S interface is responsible for the
diffusion of electron pairs in N. Superconducting-like properties are induced
in the normal metal. In particular, the conductivity of the N metal is locally
enhanced by the proximity effect. A re-entrance of the metallic conductance
occurs when all the energies involved (e.g. temperature and voltage) are small.
The relevant characteristic energy is the Thouless energy which is $\hbar$
divided by the diffusion time for an electron travelling throughout the sample.
In loop-shaped devices, a 1/T temperature-dependent oscillation of the
magnetoresistance arises with a large amplitude from the long-range coherence
of low-energy pairs.Comment: Review paper, 13 pages with 5 included epsf figures, to appear in
  Superlattices and Microstructures, minor change
Multiple Andreev reflections in diffusive SNS structures

We report new measurements on sup-gap energy structure originating from
multiple Andreev reflections in mesoscopic SNS junctions. The junctions were
fabricated in a planar geometry with high transparency superconducting contacts
of Al deposited on highly diffusive and surface d-doped n++-GaAs. For samples
with a normal GaAs region of active length 0.3um the Josephson effect with a
maximal supercurrent Ic=3mA at T=237mK was observed. The sub-gap structure was
observed as a series of local minima in the differential resistance at dc bias
voltages V=2D/ne with n=1,2,4 i.e. only the even sub-gap positions. While at
V=2D/e (n=1) only one dip is observed, the n=2, and the n=4 sub-gap structures
each consists of two separate dips in the differential resistance. The mutual
spacing of these two dips is independent of temperature, and the mutual spacing
of the n=4 dips is half of the spacing of the n=2 dips. The voltage bias
positions of the sub-gap differential resistance minima coincide with the
maxima in the oscillation amplitude when a magnetic field is applied in an
interferometer configuration, where one of the superconducting electrodes has
been replaced by a flux sensitive open loop.Comment: 20 pages, 7 figure
Conductances in normal and normal-superconductor structures

We study theoretically electronic transport through a normal metal--
superconductor (NS) interface and show that more than one conductance may be
defined, depending on the pair of chemical potentials whose difference one
chooses to relate linearly to the current. We argue that the situation is
analogous to that found for purely normal transport, where different
conductance formulae can be invoked. We revisit the problem of the "right"
conductance formula in a simple language, and analyze its extension to the case
of mesoscopic superconductivity. The well-known result that the standard
conductance of a NS interface becomes 2 (in units of $2e^2/h$) in the
transmissive limit, is viewed here in a different light. We show that it is not
directly related to the presence of Andreev reflection, but rather to a
particular choice of chemical potentials. This value of 2 is measurable because
only one single-contact resistance is involved in a typical experimental setup,
in contrast with the purely normal case, where two of them intervene. We
introduce an alternative NS conductance that diverges in the transmissive limit
due to the inability of Andreev reflection to generate a voltage drop. We
illustrate numerically how different choices of chemical potential can yield
widely differing I--V curves for a given NS interface.Comment: Minor changes have been introduced and several references have been
  added, 12 pages, submitted to special issue of ``Superlattices and
  Microstructures
Flux Confinement in Mesoscopic Superconductors

We report on flux confinement effects in superconducting submicron line, loop
and dot structures. The main idea of our study was to vary the boundary
conditions for confinement of the superconducting condensate by taking samples
of different topology and, through that, modifying the lowest Landau level
E_{LLL}(H). Since the critical temperature versus applied magnetic field
T_{c}(H) is, in fact, E_{LLL}(H) measured in temperature units, it is varied as
well when the sample topology is changed. We demonstrate that in all studied
submicron structures the shape of the T_{c}(H) phase boundary is determined by
the confinement topology in a unique way.Comment: 10 pages, 5 EPS figures, uses LaTeX's sup.sty, contribution to a
  special issue of "Superlattices and Microstructures
Proximity Effect, Andreev Reflections, and Charge Transport in
  Mesoscopic Superconducting-Semiconducting Heterostructures

In the quasi-twodimensional (Q2D) electron gas of an InAs channel between an
AlSb substrate and superconducting Niobium layers the proximity effect induces
a pair potential so that a Q2D mesoscopic
superconducting-normal-superconducting (SNS) junction forms in the channel. The
pair potential is calculated with quasiclassical Green's functions in the clean
limit. For such a junction alternating Josephson currents and current-voltage
characteristics (CVCs) are computed, using the non-equilibrium quasiparticle
wavefunctions which solve the time-dependent Bogoliubov-de Gennes Equations.
The CVCs exhibit features found experimentally by the Kroemer group: A steep
rise of the current at small voltages ("foot") changes at a "corner current" to
a much slower increase of current with higher voltages, and the zero-bias
differential resistance increases with temperature. Phase-coherent multiple
Andreev reflections and the associated Cooper pair transfers are the physical
mechanisms responsible for the oscillating Josephson currents and the CVCs.
Additional experimental findings not reproduced by the theory require model
improvements, especially a consideration of the external current leads which
should give rise to hybrid quasiparticle/collective mode excitations.Comment: 8 pages, 4 figures (consisting of 5 .ps-files), added referenc
Andreev Tunneling in Strongly Interacting Quantum Dots

We review recent work on resonant Andreev tunneling through a strongly
interacting quantum dot connected to a normal and to a superconducting lead. We
derive a general expression for the current flowing in the structure and
discuss the linear and non-linear transport in the nonperturbative regime. New
effects associated to the Kondo resonance combined with the two-particle
tunneling arise. The Kondo anomaly in the $I-V$ characteristics depends on the
relative size of the gap energy and the Kondo temperature.Comment: 8 pages, 4 figures; submitted to Superlattices and Microstructure
Nonequilibrium Josephson-like effects in wide mesoscopic S-N-S junctions

Mesoscopic superconducting-normal-metal-superconducting (S-N-S) junctions
with a large separation between the superconducting electrodes (i.e. wide
junctions) exhibit nonequilibrium supercurrents, even at temperatures for which
the equilibrium Josephson effect is exponentially small. The second harmonic of
the Josephson frequency dominates these currents, as observed in recent
experiments. A simple description of these effects, in the spirit of the
Resistively-Shunted-Junction model, is suggested here. It is used to calculate
dc I-V characteristics, and to examine the effects of various types of noise
and of external microwave radiation (Shapiro steps). It is found that the
nonequilibrium supercurrents are excited when the junction is driven by a dc
bias or an ac bias, or even by external noise. In the case of junctions which
are also long in the direction perpendicular to the current flow, thermodynamic
phase fluctuations (thermal noise) alone can drive the quasiparticles out of
local equilibrium. Magnetic flux is then predicted to be trapped in units of
Phi_0 /2 = hc/4e.Comment: 10 pages, to appear in a special issue of Superlattices &
  Microstructure
Josephson current carried by Andreev levels in superconducting quantum
  point contacts

The dc Josephson effect in a superconducting quantum point contact, where
supercurrent flows through a small number of channels, is reviewd. The central
role of Andreev levels is emphasized which carry the whole supercurrent in
short symmetric Josephson junctions including tunnel junctions. A simple
intuitive view of the dc Josephson effect in a quantum point contact is given
in terms of multiple Andreev reflections. The quantization of the critical
current in superconducting quantum point contacts is briefly discussed.Comment: 8 pages, 4 figures, submitted to Superlattices and Microstructure
Coherent transport and nonlocality in mesoscopic SNS junctions:
  anomalous magnetic interference patterns

We show that in {\em ballistic} mesoscopic SNS junctions the period of
critical current vs. magnetic flux dependence (magnetic interference pattern),
$I_c(\Phi)$, changes {\em continuously and non-monotonically} from $\Phi_0$ to
$2\Phi_0$ as the length-to-width ratio of the junction grows, or temperature
drops. In {\em diffusive} mesoscopic junctions the change is even more drastic,
with the first zero of $I_c(\Phi)$ appearing at $3\Phi_0$.
  The effect is a manifestation of nonlocal relation between the supercurrent
density and superfluid velocity in the normal part of the system, with the
characteristic scale $\xi_T = \hbar v_F/2\pi k_BT$ (ballistic limit) or
$\tilde{\xi}_T = \sqrt{\hbar D/2\pi k_BT}$ (diffusive limit), the normal metal
coherence length, and arises due to restriction of the quasiparticle phase
space near the lateral boundaries of the junction. It explains the
$2\Phi_0$-periodicity recently observed by Heida et al. (Phys. Rev. B {\bf 57},
R5618 (1998)). We obtained explicit analytical expressions for the magnetic
interference pattern for a junction with an arbitrary length-to-width ratio.
Experiments are proposed to directly observe the $\Phi_0\to 2\Phi_0$- and
$\Phi_0\to 3\Phi_0$-transitions.Comment: 13 pages, 7 figures. New results on diffusive mesoscopic SNS
  junctions included. Typo in Eq.(27) corrected. Contribution to the special
  issue of Superlattices and Microstructures on mesoscopic superconductivit
Mesoscopic superconducting disks

Using the non-linear Ginzburg-Landau (GL) eqs. type I superconducting disks
of finite radius ($R$) and thickness ($d$) are studied in a perpendicular
magnetic field. Depending on $R$ and $d$, first or second order phase
transitions are found for the normal to superconducting state. For sufficiently
large $R$ several transitions in the superconducting phase are found
corresponding to different angular momentum giant vortex states. In increasing
magnetic field the superconductor is in its ground state, while in field down
sweep it is possible to drive the system into metastable states. We also
present a quantitative analysis of the relation between the detector output and
the sample magnetization. The latter, and the incorporation of the finite
thickness of the disks, are essential in order to obtain quantitative agreement
with experiment.Comment: A brief review with new result
Novel Circuit Theory of Andreev Reflection

We review here a novel circuit theory of superconductivity. The existed
circuit theory of Andreev reflection has been revised to account for
decoherence between electrons and holes and twofold nature of the distribution
function. The description of arbitrary connectors has been elaborated. In this
way one can cope with the most of the factors that limited applicability of the
old circuit theory. We give a simple example and discuss numerical
implementation of the theory.Comment: 10 pages RevTex, 1 figure, subm. to Superlattices and Microstructure
Mesoscopic Josephson Effect

In the classical Josephson effect the phase difference across the junction is
well defined, and the supercurrent is reduced only weakly by phase diffusion.
For mesoscopic junctions with small capacitance the phase undergoes large
quantum fluctuations, and the current is also decreased by Coulomb blockade
effects. We discuss the behavior of the current-voltage characteristics in a
large range of parameters comprising the phase diffusion regime with coherent
Josephson current as well as the supercurrent peak due to incoherent Cooper
pair tunneling in the Coulomb blockade regime.Comment: 10 pages, 6 figures, submitted to Superlattices and Microstructure
Multiple Andreev reflections as a transport problem in energy space

We present an approach for analyzing the dc current in voltage biased quantum
superconducting junctions. By separating terms from different $n$-particle
processes, we find that the $n$-particle current can be mapped on the problem
of wave transport through a potential structure with $n$ barriers. We discuss
the relation between resonances in such structures and the subgap structures in
the current-voltage characteristics. At zero temperature we find, exactly, that
only processes creating real excitations contribute to the current. Our results
are valid for a general SXS-junction, where the X-region is an arbitrary
non-superconducting region described by an energy-dependent transfer matrix.Comment: 11 pages, 4 figures, submitted to Superlattices and Microstructure
Controlling Josephson transport by manipulation of Andreev levels in
  ballistic mesoscopic junctions

We discuss how to control dc Josephson current by influencing the structure
and nonequilibrium population of Andreev levels via external electrostatic
gates, external current injection and electromagnetic radiation. In particular
we will consider the "giant" Josephson current in "long" SIS tunnel junctions
and the regular and anomalous nonequilibrium Josephson currents in three
terminal SNS junctions. We will briefly discuss applications to the Josephson
field effect transistor (JOFET) and to the newly invented Josephson
interference transistor (JOINT).Comment: 10 pages, 3 figures; contribution to a special volume of
  Superlattices and Microstructures journal (ed. P.F. Bagwell
Resonant tunneling through Andreev levels

We use a semiclassical approach for analysing the tunneling transport through
a normal conductor in contact with superconducting mirrors. Our analysis of the
electron-hole propagation along semiclassical trajectories shows that resonant
transmission through Andreev levels is possible resulting in an excess,
low-energy quasiparticle contribution to the conductance. The excess
conductance oscillates with the phase difference between the superconductors
having maxima at odd multiples of $\pi$ for temperatures much below the
Thouless temperatureComment: 12 pages, 3 figures; submitted to a special volume of Superlattices
  and Microstructures on Mesoscopic Superconductivit
Resonant transport through midgap states in voltage-biased Josephson
  junctions of d-wave superconductors

We study theoretically the ac Josephson effect in voltage biased planar
junctions of d-wave superconductors. For some orientations of the
superconductors a current peak is found at finite voltage in the
current-voltage characteristics. We pick out the relevant physical processes
and write down an analytical formula for the current which clearly shows how
the midgap state acts as a resonance and produces the peak. We present a
possible explanation for the zero-bias conductance peak, recently found in
experiments on grain boundary junctions of high-temperature superconductors, in
terms of resonant transmission through midgap state of quasiparticles
undergoing multiple Andreev reflections. We note that within our framework the
zero-bias conductance peak appears in rather transparent Josephson junctions of
d-wave superconductors.Comment: 10 pages, 5 figures, Submitted to a special volume of "Superlattices
  and Microstructures
Proximity-induced transport in hybrid mesoscopic normal-superconducting
  metal structures

Using an approach based on quasiclassical Green's functions we present a
theoretical study of transport in mesoscopic S/N structures in the diffusive
limit. The subgap conductance in S/N structures with barriers (zero bias and
finite bias anomalies) are discused. We also analyse the temperature dependence
of the conductance variation $\delta S(T)$ for a Andreev interferometer. We
show that besides the well know low temperature maximum a second maximum near
$T_c$ may appear. We present the results of studies on the Josephson effect in
4 terminal S/N/S contacts and on the possible sign reversal of the Josephson
critical current.Comment: 8 pages, 5 figures, with added refrence
Nano-ploughed Josephson Junctions as on-chip Radiation Sources

A new technique is presented which enables the fabrication of highly
transparent Josephson junctions in combination with mesoscopic devices. We
utilize a modified AFM tip to plough grooves into superconducting material,
thus defining a weak link. This weak link is made within the superconducting
split-gates, which are used to electrostatically form a conventional quantum
dot and serves as a source of millimeter wave radiation around 100 GHz. We show
the characteristics of typical junctions built and discuss their high-frequency
properties. We find that the millimeter wave emission of the weak link leads to
a bolometric effect in the case of quantum point contact spectroscopy.Comment: to appear in the special issue of Superlattices and Microstructures
  on Mesoscopic Superconductivity (scheduled for May 1999
Superflow in d-wave superconductors

Superflow in a phenomenological tight-binding model for the superconducting
state of some High-temperature superconductors is discussed thoroughly. The
formalism used is explicitly gauge-invariant and currents are computed exactly
within BCS theory, going therefore beyond linear response theory. The
dependence of gap functions, current density, critical currents, and free
energy as a function of superfluid velocity for different angles and doping
concentrations is investigated. Different sources of anisotropy, like the
dispersion relation of the model, the internal symmetry of the order parameter,
and orthorhombic distortions of the lattice are also studied.Comment: 10 pages, 8 eps figures include
Current-carrying states in superconductor/insulator and
  superconductor/semiconductor superlattices in the mesoscopic regime

We discuss some of the basic theoretical aspects of current-carrying states
in superconducting superlattices with tunnel barriers in the mesoscopic regime,
when the superconducting layer thickness is small compared to the BCS coherence
length but large compared to the atomic scale. We establish the necessary
conditions for the observation of the classical Josephson effect (with
sinusoidal current-phase dependence) and derive self-consistent analytical
expressions for the critical Josephson current. These expressions are
proportional to an additional small factor and have unusual temperature
dependence as compared with the single-junction case. For certain parameter
values, the superconducting gap exhibits an exponential decrease due to
pair-breaking effect of the supercurrent. The supercurrent can completely
destroy the superconductivity of the system above a certain characteristic
temperature (lower than the transition temperature of individual layers). In
this paper, we also study the effect of intrabarrier exchange interactions. We
show that this effect is strongly enhanced compared with the single- junction
case and can manifest itself in an exponential decrease of the critical
temperature.Comment: 13 pages, ReVTeX, no figure
Mesoscopic superconductors under irradiation: Microwave spectroscopy of
  Andreev states

We show that irradiation of a voltage-biased superconducting quantum point
contact at frequencies of the order of the gap energy can remove the
suppression of subgap dc transport through Andreev levels. Quantum interference
among resonant scattering events involving photon absorption is furthermore
shown to make microwave spectroscopy of the Andreev levels feasible. We also
discuss how the same interference effect can be applied for detecting weak
electromagnetic signals up to the gap frequency, and how it is affected by
dephasing and relaxation.Comment: Submitted to a special volume of "Superlattices and Microstructures"
  on Mesoscopic Superconductivit
Excess Currents Larger than the Point Contact Limit in Normal Metal
  -Superconducting Junctions

In a point contact NS junction, perfect Andreev reflection occurs over a
range of voltages equal to the superconducting energy gap, producing an excess
current of $I_{exc} = (4/3)(2e\Delta/h)$. If the superconductor has a finite
width, rather than the infinite width of the point contact, one cannot neglect
superfluid flow inside the superconducting contact. The energy range available
for perfect Andreev reflections then becomes larger than the superconducting
gap, since superfluid flow alters the dispersion relation inside the finite
width superconductor. We find a maximum excess current of approximately
$(7/3)(2e\Delta/h)$ when the width of the superconductor is approximately 7/3
times the width of the normal metal
Ballistic Transport and Andreev Resonances in Nb-In Superconducting
  Contacts to InAs and LTG-GaAs

We have formed superconducting contacts in which Cooper pairs incident from a
thick In layer must move through a thin Nb layer to reach a semiconductor,
either InAs or low temperature grown (LTG) GaAs. The effect of pair tunneling
through the Nb layer can be seen by varying the temperature through the
critical temperature of In. Several of the In/Nb-InAs devices display a peak in
the differential conductance near zero-bias voltage, which is strong evidence
of ballistic transport across the NS interface. The differential conductance of
the In/Nb-(LTG) GaAs materials system displays conductance resonances of
McMillan-Rowell type. These resonant levels exist within a band of conducting
states inside the energy gap, formed from excess As incorporation into the
(LTG) GaAs during growth. Electrons propagating in this band of states multiply
reflect between the superconductor and a potential barrier in the GaAs
conduction band to form the conductance resonances. A scattering state theory
of the differential conductance, including Andreev reflections from the
composite In/Nb contact, accounts for most qualitative features in the data
Is the `Finite Bias Anomaly' in planar GaAs-Superconductor junctons
  caused by point-contact like structures?

We correlate transmission electron microscope (TEM) pictures of
superconducting In contacts to an AlGaAs/GaAs heterojunction with differential
conductance spectroscopy performed on the same heterojunction. Metals deposited
onto a (100) AlGaAs/GaAs heterostructure do not form planar contacts but,
during thermal annealing, grow down into the heterostructure along
crystallographic planes in pyramid-like `point contacts'. Random surface
nucleation and growth gives rise to a different interface transmission for each
superconducting point contact. Samples annealed for different times, and
therefore having different contact geometry, show variations in $dI/dV$
characteristic of ballistic transport of Cooper pairs, wave interference
between different point emitters, and different types of weak localization
corrections to Giaever tunneling. We give a possible mechanism whereby the
`finite bias anomaly' of Poirier et al. (Phys. Rev. Lett., {\bf 79}, 2105
(1997)), also observed in these samples, can arise by adding the conductance of
independent superconducting point emitters in parallel