1,117 research outputs found
Vortex manipulation in a superconducting matrix with view on applications
We show how a single flux quantum can be effectively manipulated in a
superconducting film with a matrix of blind holes. Such a sample can serve as a
basic memory element, where the position of the vortex in a [k x l] matrix of
pinning sites defines the desired combination of n bits of information
(2^n=k*l). Vortex placement is achieved by strategically applied current and
the resulting position is read-out via generated voltage between metallic
contacts on the sample. Such a device can also act as a controllable source of
a nanoengineered local magnetic field for e.g. spintronics applications
Soft vortex matter in a type-I/type-II superconducting bilayer
Magnetic flux patterns are known to strongly differ in the intermediate state
of type-I and type-II superconductors. Using a type-I/type-II bilayer we
demonstrate hybridization of these flux phases into a plethora of unique new
ones. Owing to a complicated multi-body interaction between individual
fluxoids, many different intriguing patterns are possible under applied
magnetic field, such as few-vortex clusters, vortex chains, mazes or
labyrinthal structures resembling the phenomena readily encountered in soft
matter physics. However, in our system the patterns are tunable by sample
parameters, magnetic field, current and temperature, which reveals transitions
from short-range clustering to long-range ordered phases such as parallel
chains, gels, glasses and crystalline vortex lattices, or phases where lamellar
type-I flux domains in one layer serve as a bedding potential for type-II
vortices in the other - configurations clearly beyond the soft-matter analogy
Djelovanje TMB-4 na akutno letalno trovanje miševa antikolinesterazama
Poziomek, Hackley and Steinberg (1958) and, independently, Hobbiger, O\u27Sullivan and Sadler (1958) have recently described a series of NN\u27-polymethylenebis(4-hydroxyiminomethyl-pyridinium) compounds, which are potent reactivators of cholinesterases inhibited by organophosphate antichobinesterases. The most effective compound in this series NN\u27-trimethylenebis( 4-hydroxyimino-methyl-pyridinium bromide) (TMB-4) was reported to be an effective agent in protecting animals from the lethal poisoning by methylphosphorofluoridate (SARIN), DFP and TEPP (Bay, Krop and Yates, 1958; Berry, Davies and Green, 1959; Hobbig er and Sadler, 1959). In this paper additional experiments are described, carried out to estimate the antagonism of TMB-4 toward some other organo-P-compounds. A number of specific nonphosphorus anticholinesterases are included as well.TMB-4 pokazao se uspješnim u zaštiti miševa, koji su otrovani Ietalnim dozama paraoksona, parationa, metasistoksa, neostigmina, eserina, a djelomično i R0-2-1250, dimefoksa i ditereksa. Njegovo djelovanje, međutim, ne pruža dovoljnu zaštitu miševa otrovanih OMPA-om i BW284C51
Topological phase transitions in small mesoscopic chiral p-wave superconductors
Spin-triplet chiral p-wave superconductivity is typically described by a
two-component order parameter, and as such is prone to unique emergent effects
when compared to the standard single-component superconductors. Here we present
the equilibrium phase diagram for small mesoscopic chiral p-wave
superconducting disks in the presence of magnetic field, obtained by solving
the microscopic Bogoliubov-de Gennes equations self-consistently. In the
ultra-small limit, the cylindrically-symmetric giant-vortex states are the
ground state of the system. However, with increasing sample size, the
cylindrical symmetry is broken as the two components of the order parameter
segregate into domains, and the number of fragmented domain walls between them
characterizes the resulting states. Such domain walls are topological defects
unique for the p-wave order, and constitute a dominant phase in the mesoscopic
regime. Moreover, we find two possible types of domain walls, identified by
their chirality-dependent interaction with the edge states
Boosting Monte Carlo simulations of spin glasses using autoregressive neural networks
The autoregressive neural networks are emerging as a powerful computational
tool to solve relevant problems in classical and quantum mechanics. One of
their appealing functionalities is that, after they have learned a probability
distribution from a dataset, they allow exact and efficient sampling of typical
system configurations. Here we employ a neural autoregressive distribution
estimator (NADE) to boost Markov chain Monte Carlo (MCMC) simulations of a
paradigmatic classical model of spin-glass theory, namely the two-dimensional
Edwards-Anderson Hamiltonian. We show that a NADE can be trained to accurately
mimic the Boltzmann distribution using unsupervised learning from system
configurations generated using standard MCMC algorithms. The trained NADE is
then employed as smart proposal distribution for the Metropolis-Hastings
algorithm. This allows us to perform efficient MCMC simulations, which provide
unbiased results even if the expectation value corresponding to the probability
distribution learned by the NADE is not exact. Notably, we implement a
sequential tempering procedure, whereby a NADE trained at a higher temperature
is iteratively employed as proposal distribution in a MCMC simulation run at a
slightly lower temperature. This allows one to efficiently simulate the
spin-glass model even in the low-temperature regime, avoiding the divergent
correlation times that plague MCMC simulations driven by local-update
algorithms. Furthermore, we show that the NADE-driven simulations quickly
sample ground-state configurations, paving the way to their future utilization
to tackle binary optimization problems.Comment: 13 pages, 14 figure
Enhancement of bichromatic high-harmonic generation with a high-frequency field
Using a high-frequency field superposed to a linearly polarized bichromatic
laser field composed by a wave with frequency and a wave with
frequency , we show it is possible to enhance the intensity of a
group of high harmonics in orders of magnitude. These harmonics have
frequencies about 30% higher than the monochromatic-cutoff frequency, and,
within the three-step-model framework, correspond to a set of electron
trajectories for which tunneling ionization is strongly suppressed. Particular
features in the observed enhancement suggest that the high-frequency field
provides an additional mechanism for the electron to reach the continuum. This
interpretation is supported by a time-frequency analysis of the harmonic yield.
The additional high frequency field permits the control of this group of
harmonics leaving all other sets of harmonics practically unchanged, which is
an advantage over schemes involving only bichromatic fields.Comment: 6 pages RevTex, 5 figures (ps files), Changes in text, figures,
references and equations include
Vortex-antivortex nucleation in magnetically nanotextured superconductors: Magnetic-field-driven and thermal scenarios
Within the Ginzburg-Landau formalism, we predict two novel mechanisms of
vortex-antivortex nucleation in a magnetically nanostructured superconductor.
Although counterintuitive, nucleation of vortex-antivortex pairs can be
activated in a superconducting (SC) film covered by arrays of submicron
ferromagnets (FMs) when exposed to an external homogeneous magnetic field. In
another scenario, we predict the thermal induction of vortex-antivortex
configurations in SC/FM samples. This phenomenon leads to a new type of
Little-Parks oscillations of the FM magnetization-temperature phase boundary of
the superconducting film.Comment: 4 pages, 5 figures, to appear in Physical Review Letter
Local current injection into mesoscopic superconductors for the manipulation of quantum states
We perform strategic current injection in a small mesoscopic superconductor
and control the (non)equilibrium quantum states in an applied homogeneous
magnetic field. In doing so, we realize a current-driven splitting of
multi-quanta vortices, current-induced transitions between states with
different angular momenta, and current-controlled switching between otherwise
degenerate quantum states. These fundamental phenomena form the basis for
discussed electronic and logic applications, and are confirmed in both
theoretical simulations and multiple-small-tunnel-junction transport
measurements.Comment: To appear in Physical Review Letter
Electronic properties of emergent topological defects in chiral -wave superconductivity
Chiral -wave superconductors in applied magnetic field can exhibit more
complex topological defects than just conventional superconducting vortices,
due to the two-component order parameter (OP) and the broken time-reversal
symmetry. We investigate the electronic properties of those exotic states, some
of which contain clusters of one-component vortices in chiral components of the
OP and/or exhibit skyrmionic character in the \textit{relative} OP space, all
obtained as a self-consistent solution of the microscopic Bogoliubov-de Gennes
equations. We reveal the link between the local density of states (LDOS) of the
novel topological states and the behavior of the chiral domain wall between the
OP components, enabling direct identification of those states in scanning
tunneling microscopy. For example, a skyrmion always contains a closed chiral
domain wall, which is found to be mapped exactly by zero-bias peaks in LDOS.
Moreover, the LDOS exhibits electron-hole asymmetry, which is different from
the LDOS of conventional vortex states with the same vorticity. Finally, we
present the magnetic field and temperature dependence of the properties of a
skyrmion, indicating that this topological defect can be surprisingly large in
size, and can be pinned by an artificially indented non-superconducting closed
path in the sample. These features are expected to facilitate the experimental
observation of skyrmionic states, thereby enabling experimental verification of
chirality in emerging superconducting materials
Distinct magnetic signatures of fractional vortex configurations in multiband superconductors
Vortices carrying fractions of a flux quantum are predicted to exist in
multiband superconductors, where vortex core can split between multiple
band-specific components of the superconducting condensate. Using the
two-component Ginzburg-Landau model, we examine such vortex configurations in a
two-band superconducting slab in parallel magnetic field. The fractional
vortices appear due to the band-selective vortex penetration caused by
different thresholds for vortex entry within each band-condensate, and
stabilize near the edges of the sample. We show that the resulting fractional
vortex configurations leave distinct fingerprints in the static measurements of
the magnetization, as well as in ac dynamic measurements of the magnetic
susceptibility, both of which can be readily used for the detection of these
fascinating vortex states in several existing multiband superconductors.Comment: 5 pages, 4 figure
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