352 research outputs found
Disordered Josephson junction chains: Anderson localization of normal modes and impedance fluctuations
We study the properties of the normal modes of a chain of Josephson junctions
in the simultaneous presence of disorder and absorption. We consider the
superconducting regime of small phase fluctuations and focus on the case where
the effects of disorder and absorption can be treated additively. We analyze
the frequency shift and the localization length of the modes. We also calculate
the distribution of the frequency-dependent impedance of the chain. The
distribution is Gaussian if the localization length is long compared to the
absorption length; it has a power law tail in the opposite limit.Comment: 16 pages, 8 figure
Mode engineering with a one-dimensional superconducting metamaterial
We propose a way to control the Josephson energy of a single Josephson
junction embedded in one- dimensional superconducting metamaterial: an
inhomogeneous superconducting loop, made out of a superconducting nanowire or a
chain of Josephson junctions. The Josephson energy is renormalized by the
electromagnetic modes propagating along the loop. We study the behaviour of the
modes as well as of their frequency spectrum when the capacitance and the
inductance along the loop are spatially modulated. We show that, depending on
the amplitude of the modulation, the renormalized Josephson energy is either
larger or smaller than the one found for a homogeneous loop. Using typical
experimental parameters for Josepshon junction chains and superconducting
nanowires, we conclude that this mode-engineering can be achieved with
currently available metamaterials
Circuit approach to photonic heat transport
We discuss the heat transfer by photons between two metals coupled by a
linear element with a reactive impedance. Using a simple circuit approach, we
calculate the spectral power transmitted from one resistor to the other and
find that it is determined by the photon transmission coefficient, which
depends on the impedances of the metals and the coupling element. We study the
total photonic power flow for different coupling impedances, both in the linear
regime, where the temperature difference between the metals is small, and in
the non-linear regime of large temperature differences.Comment: 6 pages, 6 figure
MICROWAVE-INDUCED RESONANT REFLECTION AND LOCALIZATION OF BALLISTIC ELECTRONS IN QUANTUM MICROCHANNELS
We show that electron transport in a ballistic microchannel supporting both
propagating and reflected modes can be completely blocked by applying a
microwave electromagnetic field. The effect is due to resonant reflection
caused by multiple coherent electron-photon scattering involving at least two
spatially localized scattering centers in the channel. With many such
scattering centers present the conductance is shown to have an irregular
dependence on bias voltage, gate voltage and frequency with irregularily spaced
dips corresponding to resonant reflection. When averaged over bias, gate
voltage or frequency the conductance will decay exponentially with channel
length in full analogy with the localization of 1D electrons caused by impurity
scattering.Comment: 4 pages, latex, 1 figure available on reques
Interference of two electrons entering a superconductor
The subgap conductivity of a normal-superconductor (NS) tunnel junction is
thought to be due to tunneling of two electrons. There is a strong interference
between these two electrons, originating from the spatial phase coherence in
the normal metal at a mesoscopic length scale and the intrinsic coherence of
the superconductor.
We evaluated the interference effect on the transport through an NS junction.
We propose the layouts to observe drastic Aharonov-Bohm and Josephson
effects.Comment: 8 pages REVTex, [PostScript] figures upon reques
Theory of coherent quantum phase-slips in Josephson junction chains with periodic spatial modulations
We study coherent quantum phase-slips which lift the ground state degeneracy
in a Josephson junction ring, pierced by a magnetic flux of the magnitude equal
to half of a flux quantum. The quantum phase-slip amplitude is sensitive to the
normal mode structure of superconducting phase oscillations in the ring
(Mooij-Sch\"on modes). These, in turn, are affected by spatial inhomogeneities
in the ring. We analyze the case of weak periodic modulations of the system
parameters and calculate the corresponding modification of the quantum
phase-slip amplitude
Adiabatic pumping in a Superconductor-Normal-Superconductor weak link
We present a formalism to study adiabatic pumping through a superconductor -
normal - superconductor weak link. At zero temperature, the pumped charge is
related to the Berry phase accumulated, in a pumping cycle, by the Andreev
bound states. We analyze in detail the case when the normal region is short
compared to the superconducting coherence length. The pumped charge turns out
to be an even function of the superconducting phase difference. Hence, it can
be distinguished from the charge transferred due to the standard Josephson
effect.Comment: 4 pages, 2 figures; Fig. 2 replaced, minor changes in the tex
Observation of transition from escape dynamics to underdamped phase diffusion in a Josephson junction
We have investigated the dynamics of underdamped Josephson junctions. In
addition to the usual crossover between macroscopic quantum tunnelling and
thermally activated (TA) behaviour we observe in our samples with relatively
small Josephson coupling E_J, for the first time, the transition from TA
behaviour to underdamped phase diffusion. Above the crossover temperature the
threshold for switching into the finite voltage state becomes extremely sharp.
We propose a (T,E_J) phase-diagram with various regimes and show that for a
proper description of it dissipation and level quantization in a metastable
well are crucial.Comment: 4 pages, 3 figure
A new representation of acid-base disturbances
The acid-base status of intensive care patients is monitored on the basis of three quantities. The graphical representation which may be of help for the monitoring task is therefore cumbersome. The classical Siggaard-Andersen acid-base chart is such a representation, but it is only suited for evaluating one acid-base status at a time and not for representing acid-base paths. A new representation, obtained after a principal components transformation is presented. It is shown that the representation is characteristic for the laboratory instrument used. Its most attractive feature is that it is distortionless with respect to the three-dimensional configuration
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