167 research outputs found
Intrinsic Josephson effect and nonequilibrium soliton structures in two-gap superconductors
We predict a new dynamic state in current-carrying superconductors with
multicomponent order parameter. If the current density J exceeds a critical
value J_t, an interband breakdown caused by charge imbalance of nonequilibrium
quasiparticles occurs. For J > J_t, the electric field penetrating from current
leads gives rise to various static and dynamic soliton phase textures, and
voltage oscillations similar to the nonstationary Josephson effect. We propose
experiments to observe these effects which would probe the multicomponent
nature of the superconducting order parameter.Comment: 4 pages, 4 figure
Coulomb correlations and coherent charge tunneling in mesoscopic coupled rings
We study the effect of a strong electron-electron (e-e) interaction in a
system of two concentric one-dimensional rings with incommensurate areas A_1
and A_2, coupled by a tunnel amplitude. For noninteracting particles the
magnetic moment (persistent current) m of the many-body ground state and first
excited states is an irregular function of the external magnetic field. In
contrast, we show that when strong e-e interactions are present the magnetic
field dependence of m becomes periodic. In such a strongly correlated system
disorder can only be caused by inter-ring charge fluctuations, controllable by
a gate voltage. The oscillation period of m is proportional to 1/(A_1 + A_2) if
fluctuations are suppressed. Coherent inter-ring tunneling doubles the period
when charge fluctuations are allowed.Comment: 4 pages, 4 eps figure
Contemporaneous XMM-Newton investigation of a giant X-ray flare and quiescent state from a cool M-class dwarf in the local cavity
We report the serendipitous detection of a giant X-ray flare from the source
2XMM J043527.2-144301 during an XMM-Newton observation of the high latitude
molecular cloud MBM20. The source has not been previously studied at any
wavelength. The X-ray flux increases by a factor of more than 52 from quiescent
state to peak of flare. A 2MASS counterpart has been identified (2MASS
J04352724-1443017), and near-infrared colors reveal a spectral type of M8-M8.5
and a distance of (67\pm 13) pc, placing the source in front of MBM20. Spectral
analysis and source luminosity are also consistent with this conclusion. The
measured distance makes this object the most distant source (by about a factor
of 4) at this spectral type detected in X-rays. The X-ray flare was
characterized by peak X-ray luminosity of ~8.2E28 erg s-1 and integrated X-ray
energy of ~2.3E32 erg. The flare emission has been characterized with a
2-temperature model with temperatures of ~10 and 46 MK (0.82 and 3.97 keV), and
is dominated by the higher temperature component.Comment: 19 pages, 5 figures; Accepted for publication on Ap
Boson and fermion dynamics in quasi-one-dimensional flat band lattices
The difference between boson and fermion dynamics in quasi-one-dimensional
lattices is studied with exact simulations of particle motion and by
calculating the persistent current in small quantum rings. We consider three
different lattices which in the tight binding model exhibit flat bands. The
physical realization is considered to be an optical lattice with bosonic or
fermionic atoms. The atoms are assumed to interact with a repulsive short range
interaction. The different statistics of bosons and fermions causes different
dynamics. Spinless fermions are easily trapped in the flat band states due to
the Pauli exclusion principle, which prevents them from interacting, while
boson are able to push each other out from the flat band states
Random phases in Bose-Einstein condensates with higher order nonlinearities
We present a statistical description of Bose-Einstein condensates with
general higher order nonlinearities. In particular, we investigate the case of
cubic-quintic nonlinearities, of particular interest for dilute condensates.
The implication of decoherence for the stability properties of the condensate
is discussed.Comment: 3 pages, no figs., to appear in Eur. Phys. J.
Many Body Correlation Corrections to Superconducting Pairing in Two Dimensions.
We demonstrate that in the strong coupling limit (the superconducting gap
is as large as the chemical potential ), which is relevant to the
high- superconductivity, the correlation corrections to the gap and
critical temperature are about 10\% of the corresponding mean field
approximation values. For the weak coupling () the correlation
corrections are very large: of the order of 100\% of the corresponding mean
field values.Comment: LaTeX 12 page
C-axis resistivity and high Tc superconductivity
Recently we had proposed a mechanism for the normal-state C-axis resistivity
of the high-T layered cuprates that involved blocking of the
single-particle tunneling between the weakly coupled planes by strong
intra-planar electron-electron scattering. This gave a C-axis resistivity that
tracks the ab-plane T-linear resistivity, as observed in the high-temperature
limit. In this work this mechanism is examined further for its implication for
the ground-state energy and superconductivity of the layered cuprates. It is
now argued that, unlike the single-particle tunneling, the tunneling of a
boson-like pair between the planes prepared in the BCS-type coherent trial
state remains unblocked inasmuch as the latter is by construction an eigenstate
of the pair annihilation operator. The resulting pair-delocalization along the
C-axis offers energetically a comparative advantage to the paired-up trial
state, and, thus stabilizes superconductivity. In this scheme the strongly
correlated nature of the layered system enters only through the blocking
effect, namely that a given electron is effectively repeatedly monitored
(intra-planarly scattered) by the other electrons acting as an environment, on
a time-scale shorter than the inter-planar tunneling time. Possible
relationship to other inter-layer pairing mechanisms proposed by several
workers in the field is also briefly discussed.Comment: typos in equations corrected, contents unchange
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