22,892 research outputs found
Topological mass generation to antisymmetric tensor matter field
We propose a mechanism to give mass to tensor matter field which preserve the
U(1) symmetry. We introduce a complex vector field that couples with the tensor
in a topological term. We also analyze the influence of the kinetic terms of
the complex vector in our mechanism.Comment: 5 pages, to appear in Europhysics Letter
Quantum phase transitions in alternating spin-(1/2, 5/2) Heisenberg chains
The ground state spin-wave excitations and thermodynamic properties of two
types of ferrimagnetic chains are investigated: the alternating spin-1/2
spin-5/2 chain and a similar chain with a spin-1/2 pendant attached to the
spin-5/2 site. Results for magnetic susceptibility, magnetization and specific
heat are obtained through the finite-temperature Lanczos method with the aim in
describing available experimental data, as well as comparison with theoretical
results from the semiclassical approximation and the low-temperature
susceptibility expansion derived from Takahashi's modified spin-wave theory. In
particular, we study in detail the temperature vs. magnetic field phase diagram
of the spin-1/2 spin-5/2 chain, in which several low-temperature quantum phases
are identified: the Luttinger Liquid phase, the ferrimagnetic plateau and the
fully polarized one, and the respective quantum critical points and crossover
lines
Quantum Properties of a Which-Way Detector
We explore quantum properties of a which-way detector using three versions of
an idealized two slit arrangements. Firstly we derive complementarity relations
for the detector; secondly we show how the "experiment" may be altered in such
a way that using single position measurement on the screen we can obtain
quantum erasure. Finally we show how to construct a superposition of "wave" and
"particle" components
Dependence of the Black-body Force on Spacetime Geometry and Topology
In this paper we compute the corrections to the black-body force (BBF)
potential due to spacetime geometry and topology. This recently discovered
attractive force on neutral atoms is caused by the thermal radiation emitted
from black bodies and here we investigate it in relativistic gravitational
systems with spherical and cylindrical symmetries. For some astrophysical
objects we find that the corrected black-body potential is greater than the
flat case, showing that this kind of correction can be quite relevant when
curved spaces are considered. Then we consider four cases: The Schwarzschild
spacetime, the global monopole, the non-relativistic infinity cylinder and the
static cosmic string. For the spherically symmetric case of a massive body, we
find that two corrections appear: One due to the gravitational modification of
the temperature and the other due to the modification of the solid angle
subtended by the atom. We apply the found results to a typical neutron star and
to the Sun. For the global monopole, the modification in the black-body
potential is of topological nature and it is due to the central solid angle
deficit that occurs in the spacetime generated by that object. In the
cylindrical case, which is locally flat, no gravitational correction to the
temperature exists, as in the global monopole case. However, we find the
curious fact that the BBF depends on the topology of the spacetime through the
modification of the azimuthal angle and therefore of the solid angle. For the
static cosmic string we find that the force is null for the zero thickness
case.Comment: 8 pages, 5 figures. Revised versio
Influence of interface potential on the effective mass in Ge nanostructures
The role of the interface potential on the effective mass of charge carriers
is elucidated in this work. We develop a new theoretical formalism using a
spatially dependent effective mass that is related to the magnitude of the
interface potential. Using this formalism we studied Ge quantum dots (QDs)
formed by plasma enhanced chemical vapour deposition (PECVD) and co-sputtering
(sputter). These samples allowed us to isolate important consequences arising
from differences in the interface potential. We found that for a higher
interface potential, as in the case of PECVD QDs, there is a larger reduction
in the effective mass, which increases the confinement energy with respect to
the sputter sample. We further understood the action of O interface states by
comparing our results with Ge QDs grown by molecular beam epitaxy. It is found
that the O states can suppress the influence of the interface potential. From
our theoretical formalism we determine the length scale over which the
interface potential influences the effective mass
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