1,868 research outputs found
A tunable macroscopic quantum system based on two fractional vortices
We propose a tunable macroscopic quantum system based on two fractional
vortices. Our analysis shows that two coupled fractional vortices pinned at two
artificially created \kappa\ discontinuities of the Josephson phase in a long
Josephson junction can reach the quantum regime where coherent quantum
oscillations arise. For this purpose we map the dynamics of this system to that
of a single particle in a double-well potential. By tuning the \kappa\
discontinuities with injector currents we are able to control the parameters of
the effective double-well potential as well as to prepare a desired state of
the fractional vortex molecule. The values of the parameters derived from this
model suggest that an experimental realisation of this tunable macroscopic
quantum system is possible with today's technology.Comment: We updated our manuscript due to a change of the focus from qubit to
macroscopic quantum effect
The AGN fuelling/feedback cycle in nearby radio galaxies - V. The cold atomic gas of NGC 3100 and its group
We present Australia Compact Telescope Array (ATCA) 21-cm observations of the
nearby low-excitation radio galaxy (LERG) NGC 3100. This is the brightest
galaxy of a loose group and hosts a young ( Myr) radio source. The ATCA
observations reveal for the first time the presence of neutral hydrogen (HI)
gas in absorption in the centre of this radio galaxy, and in emission in two
low-mass galaxies of the group and in a diffuse dark cloud in the proximity of
NGC 3100. The sensitivity to low-column density gas (
cm) allows us to reveal asymmetries in the periphery of most the
HI-detected galaxies, suggesting that tidal interactions may be on-going. The
diffuse cloud does not show a stellar counterpart down to mag/arcsec
and could be the remnant of these interactions. The analysis of the HI
absorption complex in NGC 3100 indicates that the atomic phase of the hydrogen
is distributed as its molecular phase (observed at arcsecond resolution through
several carbon monoxide emission lines). We suggest that the interactions
occurring within the group are causing turbulent cold gas clouds in the
intra-group medium to be slowly accreted towards the centre of NGC 3100. This
caused the recent formation of the cold circum-nuclear disk which is likely
sustaining the young nuclear activity.Comment: 10 pages, 7 figures; submitted to Astronomy & Astrophysic
GINZBURG-LANDAU THEORY OF VORTICES IN -WAVE SUPERCONDUCTORS
Ginzburg-Landau theory is used to study the properties of single vortices and
of the Abrikosov vortex lattice in a superconductor. For a single
vortex, the -wave order parameter has the expected four-lobe structure in a
ring around the core and falls off like at large distances. The
topological structure of the -wave order parameter consists of one
counter-rotating unit vortex, centered at the core, surrounded by four
symmetrically placed positive unit vortices. The Abrikosov lattice is shown to
have a triangular structure close to and an oblique structure at lower
temperatures. Comparison is made to recent neutron scattering data.Comment: 4 pages, REVTeX, 3 figures available upon reques
Collective responses of Bi-2212 stacked junction to 100 GHz microwave radiation under magnetic field oriented along the c-axis
We studied a response of Bi-2212 mesa type structures to 100 GHz microwave
radiation. We found that applying magnetic field of about 0.1 T across the
layers enables to observe collective Shapiro step response corresponding to a
synchronization of all 50 intrinsic Josephson junctions (IJJ) of the mesa. At
high microwave power we observed up to 10th harmonics of the fundamental
Shapiro step. Besides, we found microwave induced flux-flow step position of
which is proportional to the square root of microwave power and that can exceed
at high enough powers 1 THz operating frequency of IJJ oscillations.Comment: 11 pages including 5 figures, accepted for publication in JETP
Letter
Unusual linewidth dependence of coherent THz emission measured from intrinsic Josephson junction stacks in the hot-spot regime
We report on measurements of the linewidth {\Delta}f of THz radiation emitted
from intrinsic Josephson junction stacks, using a Nb/AlN/NbN integrated
receiver for detection. Previous resolution limited measurements indicated that
{\Delta}f may be below 1 GHz - much smaller than expected from a purely
cavity-induced synchronization. While at low bias we found {\Delta}f to be not
smaller than ? 500 MHz, at high bias, where a hotspot coexists with regions
which are still superconducting, {\Delta}f turned out to be as narrow as 23
MHz. We attribute this to the hotspot acting as a synchronizing element.
{\Delta}f decreases with increasing bath temperature, a behavior reminiscent of
motional narrowing in NMR or ESR, but hard to explain in standard
electrodynamic models of Josephson junctions.Comment: 4 figures, 5 page
Superconducting states and depinning transitions of Josephson ladders
We present analytical and numerical studies of pinned superconducting states
of open-ended Josephson ladder arrays, neglecting inductances but taking edge
effects into account. Treating the edge effects perturbatively, we find
analytical approximations for three of these superconducting states -- the
no-vortex, fully-frustrated and single-vortex states -- as functions of the dc
bias current and the frustration . Bifurcation theory is used to derive
formulas for the depinning currents and critical frustrations at which the
superconducting states disappear or lose dynamical stability as and are
varied. These results are combined to yield a zero-temperature stability
diagram of the system with respect to and . To highlight the effects of
the edges, we compare this dynamical stability diagram to the thermodynamic
phase diagram for the infinite system where edges have been neglected. We
briefly indicate how to extend our methods to include self-inductances.Comment: RevTeX, 22 pages, 17 figures included; Errata added, 1 page, 1
corrected figur
A lattice in more than two Kac--Moody groups is arithmetic
Let be an irreducible lattice in a product of n infinite irreducible
complete Kac-Moody groups of simply laced type over finite fields. We show that
if n is at least 3, then each Kac-Moody groups is in fact a simple algebraic
group over a local field and is an arithmetic lattice. This relies on
the following alternative which is satisfied by any irreducible lattice
provided n is at least 2: either is an S-arithmetic (hence linear)
group, or it is not residually finite. In that case, it is even virtually
simple when the ground field is large enough.
More general CAT(0) groups are also considered throughout.Comment: Subsection 2.B was modified and an example was added ther
The star formation histories of galaxies in different stages of pre-processing in the Fornax A group
We study the recent star formation histories of ten galaxies in the Fornax A
galaxy group, on the outskirts of the Fornax cluster. The group galaxies are
gas-rich, and their neutral atomic hydrogen (HI) was studied in detail with
observations from the MeerKAT telescope. This allowed them to be classified
into different stages of pre-processing (early, ongoing, advanced). We use
long-slit spectra obtained with the South African Large Telescope (SALT) to
analyse stellar population indicators to constrain quenching timescales and to
compare these to the HI gas content of the galaxies. The H equivalent
width, EW(H), suggest that the pre-processing stage is closely related
to the recent (< 10 Myr) specific Star Formation Rate (sSFR). The early-stage
galaxy (NGC 1326B) is not yet quenched in its outer parts, while the
ongoing-stage galaxies mostly have a distributed population of very young
stars, though less so in their outer parts. The galaxies in the advanced stage
of pre-processing show very low recent sSFR in the outer parts. Our results
suggest that NGC 1326B, FCC 35 and FCC 46 underwent significantly different
histories from secular evolution during the last Gyr. The fact that most
galaxies are on the secular evolution sequence implies that pre-processing has
a negligible effect on these galaxies compared to secular evolution. We find
EW(H) to be a useful tool for classifying the stage of pre-processing
in group galaxies. The recent sSFR and HI morphology show that galaxies in the
Fornax A vicinity are pre-processing from the outside in.Comment: 17 pages, accepted for publication in MNRA
Mean Curvature Flow on Ricci Solitons
We study monotonic quantities in the context of combined geometric flows. In
particular, focusing on Ricci solitons as the ambient space, we consider
solutions of the heat type equation integrated over embedded submanifolds
evolving by mean curvature flow and we study their monotonicity properties.
This is part of an ongoing project with Magni and Mantegazzawhich will treat
the case of non-solitonic backgrounds \cite{a_14}.Comment: 19 page
The effect of an in-plane magnetic field on the interlayer transport of quasiparticles in layered superconductors
We consider the quasiparticle c-axis conductivity in highly anisotropic
layered compounds in the presence of the magnetic field parallel to the layers.
We show that at low temperatures the quasiparticle interlayer conductivity
depends strongly on the orientation of the in-plane magnetic field if the
excitation gap has nodes on the Fermi surface. Thus measurements of the
angle-dependent c-axis (out-of-plane) magnetoresistance, as a function of the
orientation of the magnetic field in the layers, provide information on the
momentum dependence of the superconducting gap (or pseudogap) on the Fermi
surface. Clean and highly anisotropic layered superconductors seem to be the
best candidates for probing the existence and location of the nodes on the
Fermi surface.Comment: 4 pages RevTeX, including 2 PostScript figures, to appear in Phys.
Rev. Let
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