545 research outputs found
Localization Effect in a 2D Superconducting Network without Disorder
The superconducting properties of a two-dimensional superconducting wire
network with a new geometry have been measured as a function of the external
magnetic field. The extreme localization effect recently predicted for this
periodic lattice is revealed as a suppression of the critical current when the
applied magnetic field corresponds to half a flux quantum per unit cell. For
this particular magnetic field, the observed vortex state configuration is
highly disordered.Comment: 6 pages, 2 eps figures, submitted to Physica C. Title change
Voltage-induced Shapiro steps in a superconducting multi-terminal structure
When a superconducting tunnel junction at a finite voltage is irradiated with
microwaves, the interplay between the alternating Josephson current and the ac
field gives rise to steps in the dc current known as Shapiro steps. In this
work we predict that in a mesoscopic structure connected to several
superconducting terminals one can induce Shapiro-like steps in the absence of
any external radiation simply by tuning the voltages of the leads. To
illustrate this effect we make quantitative predictions for a three-terminal
structure which comprises a diffusive superconductor-normal
metal-superconductor junction and a tunneling probe, a set-up which can be
realized experimentally.Comment: revtex4, 5 pages, 5 figures, to appear in Phys. Rev.
Nanoengineered magnetic-field-induced superconductivity
The perpendicular critical fields of a superconducting film have been
strongly enhanced by using a nanoengineered lattice of magnetic dots (dipoles)
on top of the film. Magnetic-field-induced superconductivity is observed in
these hybrid superconductor / ferromagnet systems due to the compensation of
the applied field between the dots by the stray field of the dipole array. By
switching between different magnetic states of the nanoengineered field
compensator, the critical parameters of the superconductor can be effectively
controlled.Comment: 4 pages, 4 figure
Landau levels in the case of two degenerate coupled bands: kagome lattice tight-binding spectrum
The spectrum of charged particles hopping on a kagome lattice in a uniform
transverse magnetic field shows an unusual set of Landau levels at low field.
They are unusual in two respects: the lowest Landau levels are paramagnetic so
their energies decrease linearly with increasing field magnitude, and the
spacings between the levels are not equal. These features are shown to follow
from the degeneracy of the energy bands in zero magnetic field. We give a
general discussion of Landau levels in the case of two degenerate bands, and
show how the kagome lattice tight-binding model includes one special case of
this more general problem. We also discuss the consequences of this for the
behavior of the critical temperature of a kagome grid superconducting wire
network, which is the experimental system that originally motivated this work.Comment: 18 pages, 8 figure
Re-entrance of the metallic conductance in a mesoscopic proximity superconductor
We present an experimental study of the diffusive transport in a normal metal
near a superconducting interface, showing the re-entrance of the metallic
conductance at very low temperature. This new mesoscopic regime comes in when
the thermal coherence length of the electron pairs exceeds the sample size.
This re-entrance is suppressed by a bias voltage given by the Thouless energy
and can be strongly enhanced by an Aharonov Bohm flux. Experimental results are
well described by the linearized quasiclassical theory.Comment: improved version submitted to Phys. Rev. lett., 4 pages, 5 included
epsf figure
Magnetic Flux Periodic Response of Nano-perforated Ultrathin Superconducting Films
We have patterned a hexagonal array of nano-scale holes into a series of
ultrathin, superconducting Bi/Sb films with transition temperatures 2.65 K
5 K. These regular perforations give the films a phase-sensitive
periodic response to an applied magnetic field. By measuring this response in
their resistive transitions, , we are able to distinguish regimes in
which fluctuations of the amplitude, both the amplitude and phase, and the
phase of the superconducting order parameter dominate the transport. The
portion of dominated by amplitude fluctuations is larger in lower
films and thus, grows with proximity to the superconductor to
insulator transition.Comment: Revised title, abstract, text, figure
Coherent low-energy charge transport in a diffusive S-N-S junction
We have studied the current voltage characteristics of diffusive mesoscopic
Nb-Cu-Nb Josephson junctions with highly-transparent Nb-Cu interfaces. We
consider the low-voltage and high-temperature regime eV<\epsilon_{c}<k_{B}T
where epsilon_{c} is the Thouless energy. The observed excess current as well
as the observed sub-harmonic Shapiro steps under microwave irradiation suggest
the occurrence of low-energy coherent Multiple Andreev Reflection (MAR).Comment: 4 pages, 4 figures, final versio
Field-effect control of superconductivity and Rashba spin-orbit coupling in top-gated LaAlO3/SrTiO3 devices
The recent development in the fabrication of artificial oxide
heterostructures opens new avenues in the field of quantum materials by
enabling the manipulation of the charge, spin and orbital degrees of freedom.
In this context, the discovery of two-dimensional electron gases (2-DEGs) at
LAlO3/SrTiO3 interfaces, which exhibit both superconductivity and strong Rashba
spin-orbit coupling (SOC), represents a major breakthrough. Here, we report on
the realisation of a field-effect LaAlO3/SrTiO3 device, whose physical
properties, including superconductivity and SOC, can be tuned over a wide range
by a top-gate voltage. We derive a phase diagram, which emphasises a
field-effect-induced superconductor-to-insulator quantum phase transition.
Magneto-transport measurements indicate that the Rashba coupling constant
increases linearly with electrostatic doping. Our results pave the way for the
realisation of mesoscopic devices, where these two properties can be
manipulated on a local scale by means of top-gates
Two interacting Hofstadter butterflies
The problem of two interacting particles in a quasiperiodic potential is
addressed. Using analytical and numerical methods, we explore the spectral
properties and eigenstates structure from the weak to the strong interaction
case. More precisely, a semiclassical approach based on non commutative
geometry techniques permits to understand the intricate structure of such a
spectrum. An interaction induced localization effect is furthermore emphasized.
We discuss the application of our results on a two-dimensional model of two
particles in a uniform magnetic field with on-site interaction.Comment: revtex, 12 pages, 11 figure
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