38,173 research outputs found
Realization of Artificial Ice Systems for Magnetic Vortices in a Superconducting MoGe Thin-film with Patterned Nanostructures
We report an anomalous matching effect in MoGe thin films containing pairs of
circular holes arranged in such a way that four of those pairs meet at each
vertex point of a square lattice. A remarkably pronounced fractional matching
was observed in the magnetic field dependences of both the resistance and the
critical current. At the half matching field the critical current can be even
higher than that at zero field. This has never been observed before for
vortices in superconductors with pinning arrays. Numerical simulations within
the nonlinear Ginzburg-Landau theory reveal a square vortex ice configuration
in the ground state at the half matching field and demonstrate similar
characteristic features in the field dependence of the critical current,
confirming the experimental realization of an artificial ice system for
vortices for the first time.Comment: To appear in Phys. Rev. Let
A Sino-German 6cm polarisation survey of the Galactic plane - VIII. Small-diameter sources
Information of small-diameter sources is extracted from the Sino-German 6cm
polarisation survey of the Galactic plane carried out with the Urumqi 25-m
telescope. We performed two-dimensional elliptical Gaussian fits to the 6cm
maps to obtain a list of sources with total-intensity and polarised flux
densities. The source list contains 3832 sources with a fitted diameter smaller
than 16 arcmin and a peak flux density exceeding 30 mJy, so about 5 times the
rms noise, of the total-intensity data. The cumulative source count indicates
completeness for flux densities exceeding about 60 mJy. We identify 125
linearly polarised sources at 6cm with a peak polarisation flux density greater
than 10 mJy, so about 3 times the rms noise, of the polarised-intensity data.
Despite lacking compact steep spectrum sources, the 6cm catalogue lists about
20 percent more sources than the Effelsberg 21cm source catalogue at the same
angular resolution and for the same area. Most of the faint 6cm sources must
have a flat spectrum and are either HII regions or extragalactic. When compared
with the Green Bank 6cm (GB6) catalogue, we obtain higher flux densities for a
number of extended sources with complex structures. Polarised 6cm sources
density are uniformly distributed in Galactic latitude. Their number density
decreases towards the inner Galaxy. More than 80 percent of the polarised
sources are most likely extragalactic. With a few exceptions, the sources have
a higher percentage polarisation at 6cm than at 21cm. Depolarisation seems to
occur mostly within the sources with a minor contribution from the Galactic
foreground emission.Comment: A&A accepted, 9 pages, 5 figures, Tables 1 and 2 are accessible from
http://zmtt.bao.ac.cn/6cm
The sino-german 6cm polarization survey of the galactic plane: A summary
We have finished the 6cm polarization survey of the Galactic plane using the
Urumqi 25m radio telescope. It covers 10deg<l<230deg in Galactic longitude and
|b| <5deg in Galactic latitude. The new polarization maps not only reveal new
properties of the diffuse magnetized interstellar medium, but also are very
useful for studying individual objects such as Hii regions, which may act as
Faraday screens with strong regular magnetic fields inside, and supernova
remnants for their polarization properties and spectra. The high sensitivity of
the survey enables us to discover two new SNRs G178.2-4.2 and G25.3-2.1 and a
number of Hii regions.Comment: 10 pages, 1 figure. International Journal of Modern Physics:
Conference Series (IJMPCS) for Proceedings of 3rd Galileo-Xu Guangqi meetin
Driving light pulses with light in two-level media
A two-level medium, described by the Maxwell-Bloch (MB) system, is engraved
by establishing a standing cavity wave with a linearly polarized
electromagnetic field that drives the medium on both ends. A light pulse,
polarized along the other direction, then scatters the medium and couples to
the cavity standing wave by means of the population inversion density
variations. We demonstrate that control of the applied amplitudes of the
grating field allows to stop the light pulse and to make it move backward
(eventually to drive it freely). A simplified limit model of the MB system with
variable boundary driving is obtained as a discrete nonlinear Schroedinger
equation with tunable external potential. It reproduces qualitatively the
dynamics of the driven light pulse
Non-collinear magnetic structure and anisotropic magnetoelastic coupling in cobalt pyrovanadate Co2V2O7
The Co2V2O7 is recently reported to exhibit amazing magnetic field-induced
magnetization plateaus and ferroelectricity, but its magnetic ground state
remains ambiguous due to its structural complexity. Magnetometry measurements,
and time-of-flight neutron powder diffraction (NPD) have been employed to study
the structural and magnetic properties of Co2V2O7, which consists of two
non-equivalent Co sites. Upon cooling below the Ne\'el temperature TN = 6.3 K,
we observe magnetic Bragg peaks at 2K in NPD which indicated the formation of
long range magnetic order of Co2+ moments. After symmetry analysis and magnetic
structure refinement, we demonstrate that Co2V2O7 possesses a complicated
non-collinear magnetic ground state with Co moments mainly located in b-c plane
and forming a non-collinear spin-chain-like structure along the c-axis. The ab
initio calculations demonstrate that the non-collinear magnetic structure is
more stable than various ferromagnetic states at low temperature. The
non-collinear magnetic structure with canted up-up-down-down spin configuration
is considered as the origin of magnetoelectric coupling in Co2V2O7 because the
inequivalent exchange striction induced by the spin-exchange interaction
between the neighboring spins is the driving force of ferroelectricity.
Besides, it is found that the deviation of lattice parameters a and b is
opposite below TN, while the lattice parameter c and stay almost constant below
TN, evidencing the anisotropic magnetoelastic coupling in Co2V2O7.Comment: 9 pages, 8 figure
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