105 research outputs found
Current-current correlations in hybrid superconducting and normal metal multiterminal structures
We consider a hybrid system consisting of two normal metal leads weakly
connected to a superconductor. Current-current correlations of the normal leads
are studied in the tunneling limit at subgap voltages and temperatures. We find
that only two processes contribute to the cross-correlation: the crossed
Andreev reflection (emission of electrons in different leads) and the elastic
cotunneling. Both processes are possible due to the finite size of the Cooper
pair. Noise measurements can thus be used to probe directly the superconducting
wave function without the drawbacks appearing in average current measurements
where the current is dominated by direct Andreev reflection processes. By
tuning the voltages it is possible to change the sign of the cross correlation.
Quantitative predictions are presented both in the diffusive and ballistic
regimes.Comment: 7 pages, 2 Figure
New superconducting phases in field-induced organic superconductor lambda-(BETS)2FeCl4
We derive the parallel upper critical field, Hc2, as a function of the
temperature T in quasi-2D organic compound lambda-(BETS)2FeCl4, accounting for
the formation of the nonuniform LOFF state. To further check the 2D LOFF model
we propose to study the Hc2(T) curve at low T in tilted fields, where the
vortex state is described by the high Landau level functions characterized by
the index n. We predict a cascade of first order transitions between vortex
phases with different n, between phases with different types of the symmetry at
given n and the change of the superconducting transition from the second order
to the first order as FeCl4 ions are replaced partly by GaCl4 ions.Comment: 4 pages, 3 figures, to be published in PR
Domain wall superconductivity in superconductor/ferromagnet bilayers
We analyze the enhancement of the superconducting critical temperature of
superconducting/ferromagnetic bilayers due to the appearance of localized
superconducting states in the vicinity of magnetic domain walls in the
ferromagnet. We consider the case when the main mechanism of the
superconductivity destruction via the proximity effect is the exchange field.
We demonstrate that the influence of the domain walls on the superconducting
properties of the bilayer may be quite strong if the domain wall thickness is
of the order of superconducting coherence length.Comment: 8 pages, 2 figure
Inelastic scattering of a photon by a quantum phase-slip
Spontaneous decay of a single photon is a notoriously inefficient process in
nature irrespective of the frequency range. We report that a quantum phase-slip
fluctuation in high-impedance superconducting waveguides can split a single
incident microwave photon into a large number of lower-energy photons with a
near unit probability. The underlying inelastic photon-photon interaction has
no analogs in non-linear optics. Instead, the measured decay rates are
explained without adjustable parameters in the framework of a new model of a
quantum impurity in a Luttinger liquid. Our result connects circuit quantum
electrodynamics to critical phenomena in two-dimensional boundary quantum field
theories, important in the physics of strongly-correlated systems. The photon
lifetime data represents a rare example of verified and useful quantum
many-body simulation.Comment: minor revision for clarity, supplementary material is available at
www.superconducting-circuits.co
Theoretical Description of Nearly Discontinuous Transition in Superconductors with Paramagnetic Depairing
Based on a theoretical argument and Monte Carlo simulations of a
Ginzburg-Landau model derived microscopically, it is argued that, in type-II
superconductors where {\it both} the paramagnetic {\it and} orbital depairings
are important, a strong first-order transition (FOT) at expected in
the mean field (MF) approximation never occurs in real systems and changes due
to the fluctuation into a crossover. The present result explains why a {\it
nearly} discontinuous crossover at with {\it no} intrinsic hysteresis
is observed only in a clean superconducting material with a singlet pairing and
a high condensation energy such as CeCoIn.Comment: Publication version. See cond-mat/0306060 regarding a corresponding
long pape
Reduction of Pauli paramagnetic pair-breaking effect in antiferromagnetic superconductors
Antiferromagnetic superconductors in a magnetic field are studied. We examine
a mechanism which significantly reduces the Pauli paramagnetic pair-breaking
effect. The mechanism is realized even in the presence of the orbital
pair-breaking effect. We illustrate it using a three-dimensional model with an
intercalated magnetic subsystem. The upper critical field is calculated for
various parameters. It is shown that the upper critical field can reach several
times the pure Pauli paramagnetic limit. The possible relevance to the large
upper critical field observed in the heavy fermion antiferromagnetic
superconductor CePt_3Si discovered recently is briefly discussed. We try to
understand the large upper critical field in the compound CePt_3Si and
field-induced superconductivity in the compound CePb_3 within a unified
framework.Comment: 5 pages, 2 figures, revtex4, minor correction
Composite excitation of Josephson phase and spin waves in Josephson junctions with ferromagnetic insulator
Coupling of Josephson-phase and spin-waves is theoretically studied in a
superconductor/ferromagnetic insulator/superconductor (S/FI/S) junction.
Electromagnetic (EM) field inside the junction and the Josephson current
coupled with spin-waves in FI are calculated by combining Maxwell and
Landau-Lifshitz-Gilbert equations. In the S/FI/S junction, it is found that the
current-voltage (I-V) characteristic shows two resonant peaks. Voltages at the
resonant peaks are obtained as a function of the normal modes of EM field,
which indicates a composite excitation of the EM field and spin-waves in the
S/FI/S junction. We also examine another type of junction, in which a
nonmagnetic insulator (I) is located at one of interfaces between S and FI. In
such a S/I/FI/S junction, three resonant peaks appear in the I-V curve, since
the Josephson-phase couples to the EM field in the I layer.Comment: 16 pages, 5 figure
Decoupling of superconducting layers in magnetic superconductor RuSr_{2}GdCu_{2}O_{8}
We propose the model for magnetic properties of the magnetic superconductor
RuSrGdCuO, which incorporates the theory of the
superconducting/ferromagnetic multilayers. The transition line , on
which the Josephson coupled superconducting planes are decoupled, i.e. , is calculated as a function of the exchange energy . As the
result of this decoupling a nonmonotonic behavior of magnetic properties, like
the lower critical field , Josephson plasma frequency, etc. is realized
near (or by crossing) the line. The obtained results are used in
analyzing the newly discovered antiferromagnetic ruthenocuprate
RuSrGdCuO with possible weak ferromagnetic order in the RuO
planes.Comment: 12 pages, 3 figs embede
Mixed-State Thermodynamics of Superconductors with Moderately Large Paramagnetic Effects
Effects of Pauli paramagnetism on thermodynamic quantities in a vortex state,
such as the specific heat and magnetization , are studied using the
quasiclassical Eilenberger formalism. We demonstrate that with an increase of
paramagnetic depairing effect, the sigh of the curvature of the field
dependence of changes from negative to positive, and that the Maki
parameter becomes an increasing function of temperature. Our results
provide a natural explanation for the unusual field dependence of seen in
CeCoIn in terms of the paramagnetic effect.Comment: Published in J. Phys. Soc. Jpn. 74, 2181 (2005
- …