3,729 research outputs found
Correlated random fields in dielectric and spin glasses
Both orientational glasses and dipolar glasses possess an intrinsic random
field, coming from the volume difference between impurity and host ions. We
show this suppresses the glass transition, causing instead a crossover to the
low phase. Moreover the random field is correlated with the inter-impurity
interactions, and has a broad distribution. This leads to a peculiar variant of
the Imry-Ma mechanism, with 'domains' of impurities oriented by a few frozen
pairs. These domains are small: predictions of domain size are given for
specific systems, and their possible experimental verification is outlined. In
magnetic glasses in zero field the glass transition survives, because the
random fields are disallowed by time-reversal symmetry; applying a magnetic
field then generates random fields, and suppresses the spin glass transition.Comment: minor modifications, final versio
Quantum spin glass in anisotropic dipolar systems
The spin-glass phase in the \LHx compound is considered. At zero transverse
field this system is well described by the classical Ising model. At finite
transverse field deviations from the transverse field quantum Ising model are
significant, and one must take properly into account the hyperfine
interactions, the off-diagonal terms in the dipolar interactions, and details
of the full J=8 spin Hamiltonian to obtain the correct physical picture. In
particular, the system is not a spin glass at finite transverse fields and does
not show quantum criticality.Comment: 6 pages, 2 figures, to appear in J. Phys. Condens. Matter
(proceedings of the HFM2006 conference
HE 0435-1223: a wide separation quadruple QSO and gravitational lens
We report the discovery of a new gravitationally lensed QSO, at a redshift z
= 1.689, with four QSO components in a cross-shaped arrangement around a bright
galaxy. The maximum separation between images is 2.6 arcsec, enabling a
reliable decomposition of the system. Three of the QSO components have g =
19.6, while component A is about 0.6 mag brighter. The four components have
nearly identical colours, suggesting little if any dust extinction in the
foreground galaxy. The lensing galaxy is prominent in the i band, weaker in r
and not detected in g. Its spatial profile is that of an elliptical galaxy with
a scale length of 12 kpc. Combining the measured colours and a mass
model for the lens, we estimate a most likely redshift range of 0.3 < z < 0.4.
Predicted time delays between the components are \la 10 days. The QSO shows
evidence for variability, with total g band magnitudes of 17.89 and 17.71 for
two epochs separated by months. However, the relative fluxes of the
components did not change, indicating that the variations are intrinsic to the
QSO rather than induced by microlensing.Comment: 7 pages, submitted to Astronomy and Astrophysic
What are the interactions in quantum glasses?
The form of the low-temperature interactions between defects in neutral
glasses is reconsidered. We analyse the case where the defects can be modelled
either as simple 2-level tunneling systems, or tunneling rotational impurities.
The coupling to strain fields is determined up to 2nd order in the displacement
field. It is shown that the linear coupling generates not only the usual
Ising-like interaction between the rotational tunneling defect modes,
which cause them to freeze around a temperature , but also a random field
term. At lower temperatures the inversion symmetric tunneling modes are still
active - however the coupling of these to the frozen rotational modes, now via
the 2nd-order coupling to phonons, generates another random field term acting
on the inversion symmetric modes (as well as shorter-range interactions
between them). Detailed expressions for all these couplings are given.Comment: 12 pages, 2 figures. Minor modifications, published versio
Alternative Large Nc Schemes and Chiral Dynamics
We compare the dependences on the number of colors of the leading pion pion
scattering amplitudes using the single index quark field and two index quark
fields. These are seen to have different relationships to the scattering
amplitudes suggested by chiral dynamics which can explain the long puzzling
pion pion s wave scattering up to about 1 GeV. This may be interesting for
getting a better understanding of the large Nc approach as well as for
application to recently proposed technicolor models.Comment: RevTex, two-columns, 6 page
HE 0047-1756: A new gravitationally lensed double QSO
The quasar HE 0047-1756, at z=1.67, is found to be split into two images
1.44" apart by an intervening galaxy acting as a gravitational lens. The flux
ratio for the two components is roughly 3.5:1, depending slightly upon
wavelength. The lensing galaxy is seen on images obtained at 800 nm and 2.1
\mu; there is also a nearby faint object which may be responsible for some
shear. The spectra of the two quasar images are nearly identical, but the
emission line ratio between the two components scale differently from the
continuum. Moreover, the fainter component has a bluer continuum slope than the
brighter one. We argue that these small differences are probably due to
microlensing. There are hints of an Einstein ring emanating from the brighter
image toward the fainter one.Comment: 4 pages, submitted to A&A Letter
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