10,514 research outputs found
Phase mixing of shear Alfvén waves as a new mechanism for electron acceleration in collisionless, kinetic plasmas
Particle-in-cell (kinetic) simulations of shear Alfv´en wave (AW) interaction with one-dimensional, across the uniform-magnetic field, density inhomogeneity (phase mixing) in collisionless plasma were performed for the first time. As a result, a new electron acceleration mechanism is discovered. Progressive distortion of the AW front, due to the differences in local Alfv´en speed, generates electrostatic fields nearly parallel to the magnetic field, which accelerate electrons via Landau damping. Surprisingly, the amplitude decay law in the inhomogeneous regions, in the kinetic regime, is the same as in the MHD approximation described by Heyvaerts and Priest (1983 Astron. Astrophys. 117 220)
Critical exponent in the magnetization curve of quantum spin chains
The ground state magnetization curve around the critical magnetic field
of quantum spin chains with the spin gap is investigated. We propose a size
scaling method to estimate the critical exponent defined as from finite cluster calculation. The applications of the
method to the S=1 antiferromagnetic chain and S=1/2 bond alternating chain lead
to a common conclusion . The same result is derived for both edges
of the magnetization plateau of the S=3/2 antiferromagnetic chain with the
single ion anisotropy.Comment: 4 pages, Revtex, with 4 eps figure
Metamagnetism of antiferromagnetic XXZ quantum spin chains
The magnetization process of the one-dimensional antiferromagnetic Heisenberg
model with the Ising-like anisotropic exchange interaction is studied by the
exact diagonalization technique. It results in the evidence of the first-order
spin flop transition with a finite magnetization jump in the N\'eel ordered
phase for . It implies that the S=1/2 chain is an exceptional case
where the metamagnetic transition becomes second-order due to large quantum
fluctuations.Comment: 4 pages, Revtex, with 6 eps figure
Field induced transition of the S=1 antiferromagnetic chain with anisotropy
The ground state magnetization process of the S=1 antiferromagnetic chain
with the easy-axis single-ion anisotropy described by negative is
investigated. It is numerically found that a phase transition between two
different gapless phases occurs at an intermediate magnetic field between the
starting and saturation points of the magnetization for . The
transition is similar to the spin flopping, but it is second-order and not
accompanied with any significant anomalous behaviors in the magnetization
curve. We also present the phase diagrams in the m-D and H-D planes which
reveal a possible re-entrant transition.Comment: 6 pages, Revtex, with 6 eps figures, to appear in Phys. Rev. B (Sep.
1
Relativistic particle acceleration in an electron–positron plasma with a relativistic electron beam
Results from three‐dimensional electromagnetic particle simulations of an electron–positron plasma with a relativistic electron beam (γ=2) are presented. As part of the initial conditions, a poloidal magnetic field is specified, consistent with the current carried by the beam electrons. The beam undergoes pinching oscillations due to the pressure imbalance. A transverse two‐stream instability is excited with large helical perturbations. In the process, background electrons and positrons are heated and accelerated up to relativistic energy levels. Only background electrons are accelerated farther along the z direction due the synergetic effects by both the damped transverse mode and the accompanying electrostatic waves caused by the breakdown of the helical perturbations. © 1994 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70513/2/PHPAEN-1-12-4114-1.pd
Magnetically Stabilized Nematic Order I: Three-Dimensional Bipartite Optical Lattices
We study magnetically stabilized nematic order for spin-one bosons in optical
lattices. We show that the Zeeman field-driven quantum transitions between
non-nematic Mott states and quantum spin nematic states in the weak hopping
limit are in the universality class of the ferromagnetic XXZ (S=1/2) spin
model. We further discuss these transitions as condensation of interacting
magnons. The development of O(2) nematic order when external fields are applied
corresponds to condensation of magnons, which breaks a U(1) symmetry.
Microscopically, this results from a coherent superposition of two non-nematic
states at each individual site. Nematic order and spin wave excitations around
critical points are studied and critical behaviors are obtained in a dilute gas
approximation. We also find that spin singlet states are unstable with respect
to quadratic Zeeman effects and Ising nematic order appears in the presence of
any finite quadratic Zeeman coupling. All discussions are carried out for
states in three dimensional bipartite lattices.Comment: 16 pages, 3 figure
Transmission Electron Study of Heteroepitaxial Growth in the BiSrCaCuO System
Films of BiSrCaCuO and BiSrCuO have been grown using Atomic-Layer-by-Layer Molecular Beam
Epitaxy (ALL-MBE) on lattice-matched substrates. These materials have been
combined with layers of closely-related metastable compounds like BiSrCaCuO (2278) and rare-earth-doped
compounds like BiSrDyCaCuO
(Dy:2212) to form heterostructures with unique superconducting properties,
including superconductor/insulator multilayers and tunnel junctions.
Transmission electron microscopy (TEM) has been used to study the morphology
and microstructure of these heterostructures. These TEM studies shed light on
the physical properties of the films, and give insight into the growth mode of
highly anisotropic solids like BiSrCaCuO.Comment: 17 pages, submitted to J. Materials Research. Email to
[email protected] if you want to receive copies of the figure
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