3,322 research outputs found
Generation of focusing ion beams by magnetized electron sheath acceleration.
We present the first 3D fully kinetic simulations of laser driven sheath-based ion acceleration with a kilotesla-level applied magnetic field. The application of a strong magnetic field significantly and beneficially alters sheath based ion acceleration and creates two distinct stages in the acceleration process associated with the time-evolving magnetization of the hot electron sheath. The first stage delivers dramatically enhanced acceleration, and the second reverses the typical outward-directed topology of the sheath electric field into a focusing configuration. The net result is a focusing, magnetic field-directed ion source of multiple species with strongly enhanced energy and number. The predicted improvements in ion source characteristics are desirable for applications and suggest a route to experimentally confirm magnetization-related effects in the high energy density regime. We additionally perform a comparison between 2D and 3D simulation geometry, on which basis we predict the feasibility of observing magnetic field effects under experimentally relevant conditions
Detection Efficiency of Lorentz and Dispersion Types of Resonance
開始ページ、終了ページ: 冊子体のページ付
Moving embedded lattice solitons
It was recently proved that isolated unstable "embedded lattice solitons"
(ELS) may exist in discrete systems. The discovery of these ELS gives rise to
relevant questions such as the following: are there continuous families of
ELS?, can ELS be stable?, is it possible for ELS to move along the lattice?,
how do ELS interact?. The present work addresses these questions by showing
that a novel differential-difference equation (a discrete version of a complex
mKdV equation) has a two-parameter continuous family of exact ELS. The
numerical tests reveal that these solitons are stable and robust enough to
withstand collisions. The model may apply to the description of a Bose-Einstein
condensate with dipole-dipole interactions between the atoms, trapped in a deep
optical-lattice potential.Comment: 13 pages, 11 figure
Spin dynamical properties and orbital states of the layered perovskite La_2-2x_Sr_1+2x_Mn_2_O_7 (0.3 <= x < 0.5)
Low-temperature spin dynamics of the double-layered perovskite
La_2-2x_Sr_1+2x_Mn_2_O_7 (LSMO327) was systematically studied in a wide hole
concentration range (0.3 <= x < 0.5). The spin-wave dispersion, which is almost
perfectly 2D, has two branches due to a coupling between layers within a
double-layer. Each branch exhibits a characteristic intensity oscillation along
the out-of-plane direction. We found that the in-plane spin stiffness constant
and the gap between the two branches strongly depend on x. By fitting to
calculated dispersion relations and cross sections assuming Heisenberg models,
we have obtained the in-plane (J_para), intra-bilayer (J_perp) and
inter-bilayer (J') exchange interactions at each x. At x=0.30, J_para=-4meV and
J_perp=-5meV, namely almost isotropic and ferromagnetic. Upon increasing x,
J_perp rapidly approaches zero while |J_para| increases slightly, indicating an
enhancement of the planar magnetic anisotropy. At x=0.48, J_para reaches -9meV,
while J_perp turns to +1meV indicating an antiferromagnetic interaction. Such a
drastic change of the exchange interactions can be ascribed to the change of
the relative stability of the d_x^2-y^2 and d_3z^2-r^2 orbital states upon
doping. However, a simple linear combination of the two states results in an
orbital state with an orthorhombic symmetry, which is inconsistent with the
tetragonal symmetry of the crystal structure. We thus propose that an ``orbital
liquid'' state realizes in LSMO327, where the charge distribution symmetry is
kept tetragonal around each Mn site.Comment: 10 pages including 7 figure
Critical enhancement of thermopower in a chemically tuned polar semimetal MoTe
Ferroelectrics with spontaneous electric polarization play an essential role
in today's device engineering, such as capacitors and memories. Their physical
properties are further enriched by suppressing the long-range polar order, as
is exemplified by quantum paraelectrics with giant piezoelectric and dielectric
responses at low temperatures. Likewise in metals, a polar lattice distortion
has been theoretically predicted to give rise to various unusual physical
properties. So far, however, a "ferroelectric"-like transition in metals has
seldom been controlled and hence its possible impacts on transport phenomena
remain unexplored. Here we report the discovery of anomalous enhancement of
thermopower near the critical region between the polar and nonpolar metallic
phases in 1T'-MoNbTe with a chemically tunable polar
transition. It is unveiled from the first-principles calculations and
magnetotransport measurements that charge transport with strongly
energy-dependent scattering rate critically evolves towards the boundary to the
nonpolar phase, resulting in large cryogenic thermopower. Such a significant
influence of the structural instability on transport phenomena might arise from
the fluctuating or heterogeneous polar metallic states, which would pave a
novel route to improving thermoelectric efficiency.Comment: 26 pages, 4 figure
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