2,124,282 research outputs found
Competition Between Exchange and Anisotropy in a Pyrochlore Ferromagnet
The Ising-like spin ice model, with a macroscopically degenerate ground
state, has been shown to be approximated by several real materials. Here we
investigate a model related to spin ice, in which the Ising spins are replaced
by classical Heisenberg spins. These populate a cubic pyrochlore lattice and
are coupled to nearest neighbours by a ferromagnetic exchange term J and to the
local axes by a single-ion anisotropy term D. The near neighbour spin
ice model corresponds to the case D/J infinite. For finite D/J we find that the
macroscopic degeneracy of spin ice is broken and the ground state is
magnetically ordered into a four-sublattice structure. The transition to this
state is first-order for D/J > 5 and second-order for D/J < 5 with the two
regions separated by a tricritical point. We investigate the magnetic phase
diagram with an applied field along [1,0,0] and show that it can be considered
analogous to that of a ferroelectric.Comment: 7 pages, 4 figure
Dynamical symmetry breaking as the origin of the zero--resistance state in an -driven system
Under a strong drive the zero-frequency linear response dissipative
resistivity of a homogeneous state is allowed to become
negative. We show that such a state is absolutely unstable. The only
time-independent state of a system with a is characterized by
a current which almost everywhere has a magnitude fixed by the
condition that the nonlinear dissipative resistivity .
As a result, the dissipative component of the electric field vanishes. The
total current may be varied by rearranging the current pattern appropriately
with the dissipative component of the -electric field remaining zero. This
result, together with the calculation of Durst \emph{et. al.}, indicating the
existence of regimes of applied microwave field and magnetic field
where , explains the zero-resistance state observed by Mani
\emph{et. al.} and Zudov \emph{et. al.}.Comment: Published versio
First Order Phase Transition in the 3-dimensional Blume-Capel Model on a Cellular Automaton
The first order phase transition of the three-dimensional Blume Capel are
investigated using cooling algorithm which improved from Creutz Cellular
Automaton for the parameter value in the first order phase transition
region. The analysis of the data using the finite-size effect and the histogram
technique indicate that the magnetic susceptibility maxima and the specific
heat maxima increase with the system volume () at .Comment: 13 pages, 4 figure
Quantum entanglement in the NMR implementation of the Deutsch-Jozsa algorithm
A scheme to execute an n-bit Deutsch-Jozsa (D-J) algorithm using n qubits has
been implemented for up to three qubits on an NMR quantum computer. For the one
and two bit Deutsch problem, the qubits do not get entangled, hence the NMR
implementation is achieved without using spin-spin interactions. It is for the
three bit case, that the manipulation of entangled states becomes essential.
The interactions through scalar J-couplings in NMR spin systems have been
exploited to implement entangling transformations required for the three bit
D-J algorithm.Comment: 4-pages in revtex with 5 eps figure included using psfi
Reentrant Phase Transitions of the Blume-Emery-Griffiths Model for a Simple Cubic Lattice on the Cellular Automaton
The spin-1 Ising (BEG) model with the nearest-neighbour bilinear and
biquadratic interactions and single-ion anisotropy is simulated on a cellular
automaton which improved from the Creutz cellular automaton(CCA) for a simple
cubic lattice. The simulations have been made for several sets of parameters
and in the and parameter regions.
The re-entrant and double re-entrant phase transitions of the BEG model are
determined from the temperature variations of the thermodynamic quantities
(, and ). The phase diagrams characterizing phase transitions are
compared with those obtained from other methods.Comment: 12 pages 7 figure
Quantum Isometry Group for Spectral Triples with Real Structure
Given a spectral triple of compact type with a real structure in the sense of
[Dabrowski L., J. Geom. Phys. 56 (2006), 86-107] (which is a modification of
Connes' original definition to accommodate examples coming from quantum group
theory) and references therein, we prove that there is always a universal
object in the category of compact quantum group acting by orientation
preserving isometries (in the sense of [Bhowmick J., Goswami D., J. Funct.
Anal. 257 (2009), 2530-2572]) and also preserving the real structure of the
spectral triple. This gives a natural definition of quantum isometry group in
the context of real spectral triples without fixing a choice of 'volume form'
as in [Bhowmick J., Goswami D., J. Funct. Anal. 257 (2009), 2530-2572]
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