78 research outputs found
Proximity effect in the presence of Coulomb interaction and magnetic field
We consider a small metallic grain coupled to a superconductor by a tunnel
contact. We study the interplay between proximity and charging effects in the
presence of the external magnetic field. Employing the adiabatic approximation
we develop a self-consistent theory valid for an arbitrary ratio of proximity
and Coulomb strength. The magnetic field suppresses the proximity-induced
minigap in an unusual way. We find the phase diagram of the grain in the
charging energy - magnetic field plane. Two distinct states exist with
different values and magnetic field dependences of the minigap. The first-order
phase transition occurs between these two minigapped states. The transition to
the gapless state may occur by the first- or second-order mechanism depending
on the charging energy. We also calculate the tunneling density of states in
the grain. The energy dependence of this quantity demonstrates two different
gaps corresponding to the Coulomb and proximity effects. These gaps may be
separated in sufficiently high magnetic field.Comment: 11 pages (including 8 EPS figures). Version 3: extended. Final
version as published in PR
Quantum Theory of High Harmonic Generation via Above Threshold Ionization and Stimulated Recombination
Fully quantum treatment explicitly presents the high harmonic generation as a
three-stage process: above threshold ionization (ATI) is followed by the
continuum electron propagation in a laser field and subsequent stimulated
recombination back into the initial state. The contributions of all ATI
channels add up coherently. All three stages of the process are described by
simple, mostly analytical expressions. A very good quantitative agreement with
the previous calculations on the harmonic generation by H ion is
demonstrated, thus supplementing the conceptual significance of the theory with
its practical efficiency.Comment: Latex IOP stile, plus 1 figure in a PostScript fil
Ballistic transport in disordered graphene
An analytic theory of electron transport in disordered graphene in a
ballistic geometry is developed. We consider a sample of a large width W and
analyze the evolution of the conductance, the shot noise, and the full
statistics of the charge transfer with increasing length L, both at the Dirac
point and at a finite gate voltage. The transfer matrix approach combined with
the disorder perturbation theory and the renormalization group is used. We also
discuss the crossover to the diffusive regime and construct a ``phase diagram''
of various transport regimes in graphene.Comment: 23 pages, 10 figure
The differential-algebraic and bi-Hamiltonian integrability analysis of the Riemann type hierarchy revisited
A differential-algebraic approach to studying the Lax type integrability of
the generalized Riemann type hydrodynamic hierarchy is revisited, its new Lax
type representation and Poisson structures constructed in exact form. The
related bi-Hamiltonian integrability and compatible Poissonian structures of
the generalized Riemann type hierarchy are also discussed.Comment: 18 page
Multiphoton radiative recombination of electron assisted by laser field
In the presence of an intensive laser field the radiative recombination of
the continuum electron into an atomic bound state generally is accompanied by
absorption or emission of several laser quanta. The spectrum of emitted photons
represents an equidistant pattern with the spacing equal to the laser
frequency. The distribution of intensities in this spectrum is studied
employing the Keldysh-type approximation, i.e. neglecting interaction of the
impact electron with the atomic core in the initial continuum state. Within the
adiabatic approximation the scale of emitted photon frequencies is subdivided
into classically allowed and classically forbidden domains. The highest
intensities correspond to emission frequencies close to the edges of
classically allowed domain. The total cross section of electron recombination
summed over all emitted photon channels exhibits negligible dependence on the
laser field intensity.Comment: 14 pages, 5 figures (Figs.2-5 have "a" and "b" parts), Phys.Rev.A
accepted for publication. Fig.2b is presented correctl
Mesoscopic fluctuations of the supercurrent in diffusive Josephson junctions
We study mesoscopic fluctuations and weak localization correction to the
supercurrent in Josephson junctions with coherent diffusive electron dynamics
in the normal part. Two kinds of junctions are considered: a chaotic dot
coupled to superconductors by tunnel barriers and a diffusive junction with
transparent normal--superconducting interfaces. The amplitude of current
fluctuations and the weak localization correction to the average current are
calculated as functions of the ratio between the superconducting gap and the
electron dwell energy, temperature, and superconducting phase difference across
the junction. Technically, fluctuations on top of the spatially inhomogeneous
proximity effect in the normal region are described by the replicated version
of the \sigma-model. For the case of diffusive junctions with transparent
interfaces, the magnitude of mesoscopic fluctuations of the critical current
appears to be nearly 3 times larger than the prediction of the previous theory
which did not take the proximity effect into account.Comment: 19 pages, 14 figures, 2 table
Magnetic field induced polarization effects in intrinsically granular superconductors
Based on the previously suggested model of nanoscale dislocations induced
Josephson junctions and their arrays, we study the magnetic field induced
electric polarization effects in intrinsically granular superconductors. In
addition to a new phenomenon of chemomagnetoelectricity, the model predicts
also a few other interesting effects, including charge analogues of Meissner
paramagnetism (at low fields) and "fishtail" anomaly (at high fields). The
conditions under which these effects can be experimentally measured in
non-stoichiometric high-T_c superconductors are discussed.Comment: 10 pages (REVTEX), 5 EPS figures; revised version accepted for
publication in JET
Unified description of magic numbers of metal clusters in terms of the 3-dimensional q-deformed harmonic oscillator
Magic numbers predicted by a 3-dimensional q-deformed harmonic oscillator
with Uq(3)>SOq(3) symmetry are compared to experimental data for atomic
clusters of alkali metals (Li, Na, K, Rb, Cs), noble metals (Cu, Ag, Au),
divalent metals (Zn, Cd), and trivalent metals (Al, In), as well as to
theoretical predictions of jellium models, Woods-Saxon and wine bottle
potentials, and to the classification scheme using the 3n+l pseudo quantum
number. In alkali metal clusters and noble metal clusters the 3-dimensional
q-deformed harmonic oscillator correctly predicts all experimentally observed
magic numbers up to 1500 (which is the expected limit of validity for theories
based on the filling of electronic shells), while in addition it gives
satisfactory results for the magic numbers of clusters of divalent metals and
trivalent metals, thus indicating that Uq(3), which is a nonlinear extension of
the U(3) symmetry of the spherical (3-dimensional isotropic) harmonic
oscillator, is a good candidate for being the symmetry of systems of several
metal clusters. The Taylor expansions of angular momentum dependent potentials
approximately producing the same spectrum as the 3-dimensional q-deformed
harmonic oscillator are found to be similar to the Taylor expansions of the
symmetrized Woods-Saxon and wine-bottle symmetrized Woods-Saxon potentials,
which are known to provide successful fits of the Ekardt potentials.Comment: 23 pages including 7 table
Threshold Laws for the Break-up of Atomic Particles into Several Charged Fragments
The processes with three or more charged particles in the final state exhibit
particular threshold behavior, as inferred by the famous Wannier law for (2e +
ion) system. We formulate a general solution which determines the threshold
behavior of the cross section for multiple fragmentation. Applications to
several systems of particular importance with three, four and five leptons
(electrons and positrons) in the field of charged core; and two pairs of
identical particles with opposite charges are presented. New threshold
exponents for these systems are predicted, while some previously suggested
threshold laws are revised.Comment: 40 pages, Revtex, scheduled for the July issue of Phys.Rev.A (1998
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