12,929 research outputs found
Magnetoelectric polarizability and axion electrodynamics in crystalline insulators
The orbital motion of electrons in a three-dimensional solid can generate a
pseudoscalar magnetoelectric coupling , a fact we derive for the
single-particle case using a recent theory of polarization in weakly
inhomogeneous materials. This polarizability is the same parameter
that appears in the "axion electrodynamics" Lagrangian , which is known to describe the
unusual magnetoelectric properties of the three-dimensional topological
insulator (). We compute for a simple model that accesses
the topological insulator and discuss its connection to the surface Hall
conductivity. The orbital magnetoelectric polarizability can be generalized to
the many-particle wavefunction and defines the 3D topological insulator, like
the IQHE, in terms of a topological ground-state response function.Comment: 4 pages; minor changes resulting from a change in one referenc
Slow light in molecular aggregates nanofilms
We study slow light performance of molecular aggregates arranged in nanofilms
by means of coherent population oscillations (CPO). The molecular cooperative
behavior inside the aggregate enhances the delay of input signals in the GHz
range in comparison with other CPO-based devices. Moreover, the problem of
residual absorption present in CPO processes, is removed. We also propose an
optical switch between different delays by exploiting the optical bistability
of these aggregates.Comment: 4 pages, 4 figure
Magnetic phase diagram of a spin-1 condensate in two dimensions with dipole interaction
Several new features arise in the ground-state phase diagram of a spin-1
condensate trapped in an optical trap when the magnetic dipole interaction
between the atoms is taken into account along with confinement and spin
precession. The boundaries between the regions of ferromagnetic and polar
phases move as the dipole strength is varied and the ferromagnetic phases can
be modulated. The magnetization of the ferromagnetic phase perpendicular to the
field becomes modulated as a helix winding around the magnetic field direction,
with a wavelength inversely proportional to the dipole strength. This
modulation should be observable for current experimental parameters in
Rb. Hence the much-sought supersolid state, with broken continuous
translation invariance in one direction and broken global U(1) invariance,
occurs generically as a metastable state in this system as a result of dipole
interaction. The ferromagnetic state parallel to the applied magnetic field
becomes striped in a finite system at strong dipolar coupling.Comment: 11 pages, 7 figures;published versio
Bulk fields in AdS_5 from probe D7 branes
We relate bulk fields in Randall-Sundrum AdS_5 phenomenological models to the
world-volume fields of probe D7 branes in the Klebanov-Witten background of
type IIB string theory. The string constructions are described by AdS_5 X
T^{1,1} in their near-horizon geometry, with T^{1,1} a 5d compact internal
manifold that yields N=1 supersymmetry in the dual 4d gauge theory. The
effective 5d Lagrangian description derived from the explicit string
construction leads to additional features that are not usually encountered in
phenomenological model building.Comment: 23 pages, 4 figures; v2: references added; v3: equations simplified,
typos correcte
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