1,320 research outputs found
Nematicity as a route to a magnetic field-induced spin density wave order; application to the high temperature cuprates
The electronic nematic order characterized by broken rotational symmetry has
been suggested to play an important role in the phase diagram of the high
temperature cuprates. We study the interplay between the electronic nematic
order and a spin density wave order in the presence of a magnetic field. We
show that a cooperation of the nematicity and the magnetic field induces a
finite coupling between the spin density wave and spin-triplet staggered flux
orders. As a consequence of such a coupling, the magnon gap decreases as the
magnetic field increases, and it eventually condenses beyond a critical
magnetic field leading to a field-induced spin density wave order. Both
commensurate and incommensurate orders are studied, and the experimental
implications of our findings are discussed.Comment: 5 pages, 3 figure
Fractal escapes in Newtonian and relativistic multipole gravitational fields
We study the planar motion of test particles in gravitational fields produced
by an external material halo, of the type found in many astrophysical systems,
such as elliptical galaxies and globular clusters. Both the Newtonian and the
general-relativistic dynamics are examined, and in the relativistic case the
dynamics of both massive and massless particles are investigated. The halo
field is given in general by a multipole expansion; we restrict ourselves to
multipole fields of pure order, whose Newtonian potentials are homogeneous
polynomials in cartesian coordinates. A pure (n)-pole field has (n) different
escapes, one of which is chosen by the particle according to its initial
conditions. We find that the escape has a fractal dependency on the initial
conditions for (n>2) both in the Newtonian and the relativistic cases for
massive test particles, but with important differences between them. The
relativistic motion of massless particles, however, was found to be regular for
all the fields we could study. The box-counting dimension was used in each case
to quantify the sensitivity to initial conditions which arises from the
fractality of the escape route.Comment: 17 pages, 7 figures, uses REVTE
Exploring AdS Waves Via Nonminimal Coupling
We consider nonminimally coupled scalar fields to explore the Siklos
spacetimes in three dimensions. Their interpretation as exact gravitational
waves propagating on AdS restrict the source to behave as a pure radiation
field. We show that the related pure radiation constraints single out a unique
self-interaction potential depending on one coupling constant. For a vanishing
coupling constant, this potential reduces to a mass term with a mass fixed in
terms of the nonminimal coupling parameter. This mass dependence allows the
existence of several free cases including massless and tachyonic sources. There
even exists a particular value of the nonminimal coupling parameter for which
the corresponding mass exactly compensates the contribution generated by the
negative scalar curvature, producing a genuinely massless field in this curved
background. The self-interacting case is studied in detail for the conformal
coupling. The resulting gravitational wave is formed by the superposition of
the free and the self-interaction contributions, except for a critical value of
the coupling constant where a non-perturbative effect relating the strong and
weak regimes of the source appears. We establish a correspondence between the
scalar source supporting an AdS wave and a pp wave by showing that their
respective pure radiation constraints are conformally related, while their
involved backgrounds are not. Finally, we consider the AdS waves for
topologically massive gravity and its limit to conformal gravity.Comment: 26 pages, 1 figure. Minor change
Suppression of left-handed properties in disordered metamaterials
We study the effect of disorder on the effective magnetic response of
composite left-handed metamaterials and their specific properties such as
negative refraction. We show that relatively weak disorder in the split-ring
resonators can reduce and even completely eliminate the frequency domain where
the composite material demonstrates the left-handed properties. We introduce
the concept of the order parameter to describe novel physics of this effect.Comment: 4 pages, 2 figure
Superconducting quantum phase transitions tuned by magnetic impurity and magnetic field in ultrathin a-Pb films
Superconducting quantum phase transitions tuned by disorder (d), paramagnetic
impurity (MI) and perpendicular magnetic field (B) have been studied in
homogeneously disordered ultrathin a-Pb films. The MI-tuned transition is
characterized by progressive suppression of the critical temperature to zero
and a continuous transition to a weakly insulating normal state with increasing
MI density. In all important aspects, the d-tuned transition closely resembles
the MI-tuned transition and both appear to be fermionic in nature. The B-tuned
transition is qualitatively different and probably bosonic. In the critical
region it exhibits transport behavior that suggests a B-induced mesoscale phase
separation and presence of Cooper pairing in the insulating state.Comment: 17 pages, 4 figure
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