1,060 research outputs found
Phonon superradiance and phonon laser effect in nanomagnets
We show that the theory of spin-phonon processes in paramagnetic solids must
take into account the coherent generation of phonons by the magnetic centers.
This effect should drastically enhance spin-phonon rates in nanoscale
paramagnets and in crystals of molecular nanomagnets.Comment: 4 PR pages, 1 Figur
Monte Carlo study of the two-dimensional site-diluted dipolar Ising model
By tempered Monte Carlo simulations, we study 2D site-diluted dipolar Ising
systems. Dipoles are randomly placed on a fraction x of all L^2 sites in a
square lattice, and point along a common crystalline axis. For x_c< x<=1, where
x_c = 0.79(5), we find an antiferromagnetic phase below a temperature which
vanishes as x approaches x_c from above. At lower values of x, we study (i)
distributions of the spin--glass (SG) overlap q, (ii) their relative mean
square deviation Delta_q^2 and kurtosis and (iii) xi_L/L, where xi_L is a SG
correlation length. From their variation with temperature and system size, we
find that the paramagnetic phase covers the entire T>0 range. Our results
enable us to obtain an estimate of the critical exponent associated to the
correlation length at T=0, 1/nu=0.35(10).Comment: 10 LaTeX pages, 10 figures, 1 table
Conserved Growth on Vicinal Surfaces
A crystal surface which is miscut with respect to a high symmetry plane
exhibits steps with a characteristic distance. It is argued that the continuum
description of growth on such a surface, when desorption can be neglected, is
given by the anisotropic version of the conserved KPZ equation (T. Sun, H. Guo,
and M. Grant, Phys. Rev. A 40, 6763 (1989)) with non-conserved noise. A
one--loop dynamical renormalization group calculation yields the values of the
dynamical exponent and the roughness exponent which are shown to be the same as
in the isotropic case. The results presented here should apply in particular to
growth under conditions which are typical for molecular beam epitaxy.Comment: 10 pages, uses revte
Bohr-Sommerfeld quantization of spin Hamiltonians
The Bohr-Sommerfeld rule for a spin system is obtained, including the first
quantum corrections. The rule applies to both integer and half-integer spin,
and respects Kramers degeneracy for time-reversal invariant systems. It is
tested for various models, in particular the Lipkin-Meshkov-Glick model, and
found to agree very well with exact results.Comment: Revtex 4, no figures, 1 tabl
Ordering in a frustrated pyrochlore antiferromagnet proximate to a spin liquid
We perform a general study of spin ordering on the pyrochlore lattice with a
3:1 proportionality of two spin polarizations. Equivalently, this describes
valence bond solid conformations of a quantum dimer model on the diamond
lattice. We determine the set of likely low temperature ordered phases, on the
assumption that the ordering is weak, i.e the system is close to a ``U(1)''
quantum spin liquid in which the 3:1 proportionality is maintained but the
spins are strongly fluctuating. The nature of the 9 ordered states we find is
determined by a ``projective symmetry'' analysis. All the phases exhibit
translational and rotational symmetry breaking, with an enlarged unit cell
containing 4 to 64 primitive cells of the underlying pyrochlore. The simplest
of the 9 phases is the same ``R'' state found earlier in a theoretical study of
the ordering on the magnetization plateau in the materials \cdaf and
\hgaf. We suggest that the spin/dimer model proposed therein undergoes a direct
transition from the spin liquid to the R state, and describe a field theory for
the universal properties of this critical point, at zero and non-zero
temperatures
Influence of lattice distortions in classical spin systems
We investigate a simple model of a frustrated classical spin chain coupled to
adiabatic phonons under an external magnetic field. A thorough study of the
magnetization properties is carried out both numerically and analytically. We
show that already a moderate coupling with the lattice can stabilize a plateau
at 1/3 of the saturation and discuss the deformation of the underlying lattice
in this phase. We also study the transition to saturation where either a first
or second order transition can occur, depending on the couplings strength.Comment: Submitted to Phys. Rev.
Floating Phase in 1D Transverse ANNNI Model
To study the ground state of ANNNI chain under transverse field as a function
of frustration parameter and field strength , we present here
two different perturbative analyses. In one, we consider the (known) ground
state at and as the unperturbed state and treat an
increase of the field from 0 to coupled with an increase of
from 0.5 to as perturbation. The first order perturbation
correction to eigenvalue can be calculated exactly and we could conclude that
there are only two phase transition lines emanating from the point
, . In the second perturbation scheme, we consider the
number of domains of length 1 as the perturbation and obtain the zero-th order
eigenfunction for the perturbed ground state. From the longitudinal spin-spin
correlation, we conclude that floating phase exists for small values of
transverse field over the entire region intermediate between the ferromagnetic
phase and antiphase.Comment: 11 pages, 11 figure
Measurability of the tidal polarizability of neutron stars in late-inspiral gravitational-wave signals
The gravitational wave signal from a binary neutron star inspiral contains
information on the nuclear equation of state. This information is contained in
a combination of the tidal polarizability parameters of the two neutron stars
and is clearest in the late inspiral, just before merger. We use the recently
defined tidal extension of the effective one-body formalism to construct a
controlled analytical description of the frequency-domain phasing of neutron
star inspirals up to merger. Exploiting this analytical description we find
that the tidal polarizability parameters of neutron stars can be measured by
the advanced LIGO-Virgo detector network from gravitational wave signals having
a reasonable signal-to-noise ratio of . This measurability result
seems to hold for all the nuclear equations of state leading to a maximum mass
larger than . We also propose a promising new way of extracting
information on the nuclear equation of state from a coherent analysis of an
ensemble of gravitational wave observations of separate binary merger events.Comment: 28 pages, 6 figures. Submitted to Phys. Rev.
Growth of Patterned Surfaces
During epitaxial crystal growth a pattern that has initially been imprinted
on a surface approximately reproduces itself after the deposition of an integer
number of monolayers. Computer simulations of the one-dimensional case show
that the quality of reproduction decays exponentially with a characteristic
time which is linear in the activation energy of surface diffusion. We argue
that this life time of a pattern is optimized, if the characteristic feature
size of the pattern is larger than , where is the surface
diffusion constant, the deposition rate and the surface dimension.Comment: 4 pages, 4 figures, uses psfig; to appear in Phys. Rev. Let
A Spin Model for Investigating Chirality
Spin chirality has generated great interest recently both from possible
applications to flux phases and intrinsically, as an example of a several-site
magnetic order parameter that can be long-ranged even where simpler order
parameters are not. Previous work (motivated by the flux phases) has focused on
antiferromagnetic chiral order; we construct a model in which the chirality
orders ferromagnetically and investigate the model's behavior as a function of
spin. Enlisting the aid of exact diagonalization, spin-waves, perturbation
theory, and mean fields, we conclude that the model likely has long-ranged
chiral order for spins 1 and greater and no non-trivial chiral order for spin
1/2.Comment: uuencoded gzipped tarred plain tex fil
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