1,186 research outputs found
Coupled superconductors and beyond
This paper describes the events leading to the discovery of coupled
superconductors, the author's move in the 1970s to a perspective where mind
plays a role comparable to matter, and the remarkable hostility sometimes
encountered by those who venture into unconventional areas.Comment: Invited paper for special issue of Low Temperature Physics/Fizika
Nizkikh Temperatur devoted to "Quantum Coherent Effects in Superconductors
and New Materials". 6pp. v5: open-access published versio
Giant mass and anomalous mobility of particles in fermionic systems
We calculate the mobility of a heavy particle coupled to a Fermi sea within a
non-perturbative approach valid at all temperatures. The interplay of particle
recoil and of strong coupling effects, leading to the orthogonality catastrophe
for an infinitely heavy particle, is carefully taken into account. We find two
novel types of strong coupling effects: a new low energy scale and
a giant mass renormalization in the case of either near-resonant scattering or
a large transport cross section . The mobility is shown to obey two
different power laws below and above . For ,
where is the Fermi wave length, an exponentially large effective
mass suppresses the mobility.Comment: 4 pages, 4 figure
Synchronization of active mechanical oscillators by an inertial load
Motivated by the operation of myogenic (self-oscillatory) insect flight
muscle, we study a model consisting of a large number of identical oscillatory
contractile elements joined in a chain, whose end is attached to a damped
mass-spring oscillator. When the inertial load is small, the serial coupling
favors an antisynchronous state in which the extension of one oscillator is
compensated by the contraction of another, in order to preserve the total
length. However, a sufficiently massive load can sychronize the oscillators and
can even induce oscillation in situations where isolated elements would be
stable. The system has a complex phase diagram displaying quiescent,
synchronous and antisynchrononous phases, as well as an unsual asynchronous
phase in which the total length of the chain oscillates at a different
frequency from the individual active elements.Comment: 5 pages, 4 figures, To appear in Phys. Rev. Let
Experimental Designs for Binary Data in Switching Measurements on Superconducting Josephson Junctions
We study the optimal design of switching measurements of small Josephson
junction circuits which operate in the macroscopic quantum tunnelling regime.
Starting from the D-optimality criterion we derive the optimal design for the
estimation of the unknown parameters of the underlying Gumbel type
distribution. As a practical method for the measurements, we propose a
sequential design that combines heuristic search for initial estimates and
maximum likelihood estimation. The presented design has immediate applications
in the area of superconducting electronics implying faster data acquisition.
The presented experimental results confirm the usefulness of the method. KEY
WORDS: optimal design, D-optimality, logistic regression, complementary log-log
link, quantum physics, escape measurement
Voltage rectification by a SQUID ratchet
We argue that the phase across an asymmetric dc SQUID threaded by a magnetic
flux can experience an effective ratchet (periodic and asymmetric) potential.
Under an external ac current, a rocking ratchet mechanism operates whereby one
sign of the time derivative of the phase is favored. We show that there exists
a range of parameters in which a fixed sign (and, in a narrower range, even a
fixed value) of the average voltage across the ring occurs, regardless of the
sign of the external current dc component.Comment: 4 pages, 4 EPS figures, uses psfig.sty. Revised version, to appear in
Physical Review Letters (26 August 1996
Josephson Effect in Fulde-Ferrell-Larkin-Ovchinnikov Superconductors
Due to the difference in the momenta of the superconducting order parameters,
the Josephson current in a Josephson junction between a
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductor and a conventional BCS
superconductor is suppressed. We show that the Josephson current may be
recovered by applying a magnetic field in the junction. The field strength and
direction at which the supercurrent recovery occurs depend upon the momentum
and structure of the order parameter in the FFLO state. Thus the Josephson
effect provides an unambiguous way to detect the existence of an FFLO state,
and to measure the momentum of the order parameter.Comment: 4 pages with one embedded eps figur
Non-linear microwave impedance of short and long Josephson Junctions
The non-linear dependence on applied field () or current () of the microwave (ac) impedance of both
short and long Josephson junctions is calculated under a variety of excitation
conditions. The dependence on the junction width is studied, for both field
symmetric (current anti-symmetric) and field anti-symmetric (current symmetric)
excitation configurations.The resistance shows step-like features every time a
fluxon (soliton) enters the junction, with a corresponding phase slip seen in
the reactance. For finite widths the interference of fluxons leads to some
interesting effects which are described. Many of these calculated results are
observed in microwave impedance measurements on intrinsic and fabricated
Josephson junctions in the high temperature superconductors, and new effects
are suggested. When a field () or current () is applied,
interesting phase locking effects are observed in the ac impedance
. In particular an almost periodic dependence on the dc bias is
seen similar to that observed in microwave experiments at very low dc field
bias. These results are generic to all systems with a potential
in the overdamped limit and subjected to an ac drive.Comment: 7 pages, 11 figure
The transition temperature of the dilute interacting Bose gas
We show that the critical temperature of a uniform dilute Bose gas must
increase linearly with the s-wave scattering length describing the repulsion
between the particles. Because of infrared divergences, the magnitude of the
shift cannot be obtained from perturbation theory, even in the weak coupling
regime; rather, it is proportional to the size of the critical region in
momentum space. By means of a self-consistent calculation of the quasiparticle
spectrum at low momenta at the transition, we find an estimate of the effect in
reasonable agreement with numerical simulations.Comment: 4 pages, Revtex, to be published in Physical Review Letter
Pion Propagation near the QCD Chiral Phase Transition
We point out that, in analogy with spin waves in antiferromagnets, all
parameters describing the real-time propagation of soft pions at temperatures
below the QCD chiral phase transition can be expressed in terms of static
correlators. This allows, in principle, the determination of the soft pion
dispersion relation on the lattice. Using scaling and universality arguments,
we determine the critical behavior of the parameters of pion propagation. We
predict that when the critical temperature is approached from below, the pole
mass of the pion drops despite the growth of the pion screening mass. This fact
is attributed to the decrease of the pion velocity near the phase transition.Comment: 8 pages (single column), RevTeX; added references, version to be
published in PR
Tuning a Josephson junction through a quantum critical point
We tune the barrier of a Josephson junction through a zero-temperature
metal-insulator transition and study the thermodynamic behavior of the junction
in the proximity of the quantum-critical point. We examine a
short-coherence-length superconductor and a barrier (that is described by a
Falicov-Kimball model) using the local approximation and dynamical mean-field
theory. The inhomogeneous system is self-consistently solved by performing a
Fourier transformation in the planar momentum and exactly inverting the
remaining one-dimensional matrix with the renormalized perturbation expansion.
Our results show a delicate interplay between oscillations on the scale of the
Fermi wavelength and pair-field correlations on the scale of the coherence
length, variations in the current-phase relationship, and dramatic changes in
the characteristic voltage as a function of the barrier thickness or
correlation strength (which can lead to an ``intrinsic'' pinhole effect).Comment: 16 pages, 15 figures, ReVTe
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