8,293 research outputs found
On the stability and growth of single myelin figures
Myelin figures are long thin cylindrical structures that typically grow as a
dense tangle when water is added to the concentrated lamellar phase of certain
surfactants. We show that, starting from a well-ordered initial state, single
myelin figures can be produced in isolation thus allowing a detailed study of
their growth and stability. These structures grow with their base at the
exposed edges of bilayer stacks from which material is transported into the
myelin. Myelins only form and grow in the presence of a driving stress; when
the stress is removed, the myelins retract.Comment: 4 pages, 8 figures. Revised version, 1 new figure, additional
reference
Spin-orbit coupling induced by a mass gradient
The existence of a spin-orbit coupling (SOC) induced by the gradient of the
effective mass in low-dimensional heterostructures is revealed. In structurally
asymmetric quasi-two-dimensional semiconductor heterostructures the presence of
a mass gradient across the interfaces results in a SOC which competes with the
SOC created by the electric field in the valence band. However, in graded
quantum wells subjected to an external electric field, the mass-gradient
induced SOC can be finite even when the electric field in the valence band
vanishes.Comment: 4 pages, 2 figures, 1 tabl
Zitterbewegung is not an observable
It has recently been claimed that Zitterbewegung has been observed. However,
we argue that it is not an observable and that the authors' observations must
be reinterpreted
Slow Excitation Trapping in Quantum Transport with Long-Range Interactions
Long-range interactions slow down the excitation trapping in quantum
transport processes on a one-dimensional chain with traps at both ends. This is
counter intuitive and in contrast to the corresponding classical processes with
long-range interactions, which lead to faster excitation trapping. We give a
pertubation theoretical explanation of this effect.Comment: 4 pages, 3 figure
Theory of the thermoelectricity of intermetallic compounds with Ce or Yb ions
The thermoelectric properties of intermetallic compounds with Ce or Yb ions
are explained by the single-impurity Anderson model which takes into account
the crystal-field splitting of the 4{\it f} ground-state multiplet, and assumes
a strong Coulomb repulsion which restricts the number of {\it f} electrons or
{\it f} holes to for Ce and for Yb ions. Using
the non-crossing approximation and imposing the charge neutrality constraint on
the local scattering problem at each temperature and pressure, the excitation
spectrum and the transport coefficients of the model are obtained. The
thermopower calculated in such a way exhibits all the characteristic features
observed in Ce and Yb intermetallics. Calculating the effect of pressure on
various characteristic energy scales of the model, we obtain the phase
diagram which agrees with the experimental data on CeRuSi,
CeCuSi, CePdSi, and similar compounds. The evolution of the
thermopower and the electrical resistance as a function of temperature,
pressure or doping is explained in terms of the crossovers between various
fixed points of the model and the redistribution of the single-particle
spectral weight within the Fermi window.Comment: 13 pages, 11 figure
Invariant expansion for the trigonal band structure of graphene
We present a symmetry analysis of the trigonal band structure in graphene,
elucidating the transformational properties of the underlying basis functions
and the crucial role of time-reversal invariance. Group theory is used to
derive an invariant expansion of the Hamiltonian for electron states near the K
points of the graphene Brillouin zone. Besides yielding the characteristic
k-linear dispersion and higher-order corrections to it, this approach enables
the systematic incorporation of all terms arising from external electric and
magnetic fields, strain, and spin-orbit coupling up to any desired order.
Several new contributions are found, in addition to reproducing results
obtained previously within tight-binding calculations. Physical ramifications
of these new terms are discussed.Comment: 10 pages, 1 figure; expanded version with more details and additional
result
meson in dense matter
We study the properties of mesons in nuclear matter using a
unitary approach in coupled channels within the framework of the local hidden
gauge formalism and incorporating the decay channel in matter. The
in-medium interaction accounts for Pauli blocking effects and
incorporates the self-energy in a self-consistent manner. We also
obtain the (off-shell) spectral function and analyze its behaviour
at finite density and momentum. At normal nuclear matter density, the meson feels a moderately attractive potential while the width
becomes five times larger than in free space. We estimate the transparency
ratio of the reaction, which we propose as
a feasible scenario at present facilities to detect the changes of the
properties of the meson in the nuclear medium.Comment: 26 pages, 9 figures, one new section added, version published in
Phys. ReV. C, http://link.aps.org/doi/10.1103/PhysRevC.82.04521
An explanation of the as a bound state
We use the interaction in the hidden gauge formalism to
dynamically generate and resonances. We show,
through a comparison of the results from this analysis and from a quark model
study with data, that the
and resonances can be assigned to bound
states. More precisely the can be interpreted as a
bound state whereas the and
may contain an important component. This
interpretation allows for a solution of a long-standing puzzle concerning the
description of these resonances in constituent quark models. In addition we
also obtain degenerate states but their
assignment to experimental resonances is more uncertain.Comment: 19 pags, 8 fig
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