168 research outputs found
Multidomain switching in the ferroelectric nanodots
Controlling the polarization switching in the ferroelectric nanocrystals,
nanowires and nanodots has an inherent specificity related to the emergence of
depolarization field that is associated with the spontaneous polarization. This
field splits the finite-size ferroelectric sample into polarization domains.
Here, based on 3D numerical simulations, we study the formation of 180 polarization domains in a nanoplatelet, made of uniaxial ferroelectric
material, and show that in addition to the polarized monodomain state, the
multidomain structures, notably of stripe and cylindrical shapes, can arise and
compete during the switching process. The multibit switching protocol between
these configurations may be realized by temperature and field variations
Broadband spin-controlled focusing via logarithmic-spiral nanoslits of varying width
This work presents analytical, numerical and experimental demonstrations of light diffracted through a logarithmic spiral (LS) nanoslit, which forms a type of switchable and focus-tunable structure. Owing to a strong dependence on the incident photon spin, the proposed LS-nanoslit converges incoming light of opposite handedness (to that of the LS-nanoslit) into a confined subwavelength spot, while it shapes light with similar chirality into a donut-like intensity profile. Benefitting from the varying width of the LS-nanoslit, different incident wavelengths interfere constructively at different positions, i.e., the focal length shifts from 7.5 μm (at λ = 632.8 nm) to 10 μm (at λ = 488 nm), which opens up new opportunities for tuning and spatially separating broadband light at the micrometer scale
Antiferromagnetism and Superconductivity in UPt_3
The short ranged antiferromagnetism recently seen in UPt_3 is proved
incompatible with two dimensional (2D) order parameter models that take the
antiferromagnetism as a symmetry breaking field. To adjust to the local moment
direction, the order parameter twists over very long length scales as per the
Imry-Ma argument. A variational solution to the Ginzburg-Landau equations is
used to study the nature of the short ranged order. Although there are still
two transitions, the lower one is of first order -- in contradiction to
experiments. It is shown that the latent heat predicted by the 2D models at the
lower transition is too large not to have been seen. A simple periodic model is
numerically studied to show that the lower transition can not be a crossover
either.Comment: To appear in Journal of Physics: Condensed Matter. 9 pages, 2 figure
Generating Tesla magnetic pulses in plasmonic nanostructures
Bimetallic plasmonic ring resonators illuminated by femtosecond laser pulses generate transient subpicosecond thermoelectric currents and nanoconfined Tesla-scale magnetic fields
Controlling light-with-light without nonlinearity
According to Huygens' superposition principle, light beams traveling in a
linear medium will pass though one another without mutual disturbance. Indeed,
it is widely held that controlling light signals with light requires intense
laser fields to facilitate beam interactions in nonlinear media, where the
superposition principle can be broken. We demonstrate here that two coherent
beams of light of arbitrarily low intensity can interact on a metamaterial
layer of nanoscale thickness in such a way that one beam modulates the
intensity of the other. We show that the interference of beams can eliminate
the plasmonic Joule losses of light energy in the metamaterial or, in contrast,
can lead to almost total absorbtion of light. Applications of this phenomenon
may lie in ultrafast all-optical pulse-recovery devices, coherence filters and
THz-bandwidth light-by-light modulators
The optical microscopy with virtual image breaks a record: 50-nm resolution imaging is demonstrated
We demonstrate a new 'microsphere nanoscope' that uses ordinary SiO2
microspheres as superlenses to create a virtual image of the object in near
field. The magnified virtual image greatly overcomes the diffraction limit. We
are able to resolve clearly 50-nm objects under a standard white light source
in both transmission and reflection modes. The resolution achieved for white
light opens a new opportunity to image viruses, DNA and molecules in real time
Magnetic skyrmion lattices in heavy fermion superconductor UPt3
Topological analysis of nearly SO(3)_{spin} symmetric Ginzburg--Landau
theory, proposed for UPt by Machida et al, shows that there exists a new
class of solutions carrying two units of magnetic flux: the magnetic skyrmion.
These solutions do not have singular core like Abrikosov vortices and at low
magnetic fields they become lighter for strongly type II superconductors.
Magnetic skyrmions repel each other as at distances much larger then the
magnetic penetration depth , forming a relatively robust triangular
lattice. The magnetic induction near is found to increase as
. This behavior agrees well with experiments.Comment: 4 pages, 2 figures, 2 column format; v2:misprint in the title is
correcte
Reduction of Pauli paramagnetic pair-breaking effect in antiferromagnetic superconductors
Antiferromagnetic superconductors in a magnetic field are studied. We examine
a mechanism which significantly reduces the Pauli paramagnetic pair-breaking
effect. The mechanism is realized even in the presence of the orbital
pair-breaking effect. We illustrate it using a three-dimensional model with an
intercalated magnetic subsystem. The upper critical field is calculated for
various parameters. It is shown that the upper critical field can reach several
times the pure Pauli paramagnetic limit. The possible relevance to the large
upper critical field observed in the heavy fermion antiferromagnetic
superconductor CePt_3Si discovered recently is briefly discussed. We try to
understand the large upper critical field in the compound CePt_3Si and
field-induced superconductivity in the compound CePb_3 within a unified
framework.Comment: 5 pages, 2 figures, revtex4, minor correction
Unconventional Pairing in Heavy Fermion Metals
The Fermi-liquid theory of superconductivity is applicable to a broad range
of systems that are candidates for unconventional pairing. Fundamental
differences between unconventional and conventional anisotropic superconductors
are illustrated by the unique effects that impurities have on the
low-temperature transport properties of unconventional superconductors. For
special classes of unconventional superconductors the low-temperature transport
coefficients are {\it universal}, i.e. independent of the impurity
concentration and scattering phase shift. The existence of a universal limit
depends on the symmetry of the order parameter and is achieved at low
temperatures , where is the bandwidth
of the impurity induced Andreev bound states. In the case of UPt thermal
conductivity measurements favor an or ground state.
Measurements at ultra-low temperatures should distinguish different pairing
states.Comment: 8 pages in a LaTex (3.0) file plus 5 Figures in PostScript. To appear
in the Proceedings of the XXI International Conference on Low Temperature
Physics held in Prague, 8-14 August 199
- …