1,600 research outputs found
Solvent Driven Formation of Bolaamphiphilic Vesicles
We show that a spontaneous bending of single layer bolaamphiphiles results
from the frustration due to the competition between core-core and tail-solvent
interactions. We find that spherical vesicles are stable under rather general
assumptions on these interactions described within the Flory-Huggins theory. We
consider also the deformation of the vesicles in an external magnetic field
that has been recently experimentally observed.Comment: J. Phys. Chem. B, accepte
Nonperturbative anharmonic phenomena in crystal lattice dynamics
Slow dynamics of energy transfer between different phonon modes under the
resonance conditions is considered. It may result in new effects in the
inelastic and quasielastic neutron scattering spectra.Comment: Contribution to the proceedings of the 3rd International Symposium on
Slow Dynamics in Complex Systems (Sendai, Japan,November 3-8, 2003), to be
published in AIP Conference series, 200
An dynamical-mean-field-theory investigation of specific heat and electronic structure of and -plutonium
We have carried out a comparative study of the electronic specific heat and
electronic structure of and -plutonium using dynmical mean
field theory (DMFT). We use the perturbative T-matrix and fluctuating exchange
(T-matrix FLEX) as a quantum impurity solver. We considered two different
physical pictures of plutonoium. In the first, , the perturbative
treatment of electronic correlations has been carried out around the
non-magnetic (LDA) Hamiltonian, which results in an f occupation around a bit
above . In the second, , plutonium is viewed as being close
to an configuration, and perturbation theory is carried out around the
(LDA+U) starting point bit below . In the latter case the electronic
specific heat coefficient attains a smaller value in -Pu than
in -Pu, in contradiction to experiment, while in the former case our
calculations reproduce the experimentally observed large increase of
in -Pu as compared to the phase. This enhancement of the
electronic specific heat coefficient in -Pu is due to strong electronic
correlations present in this phase, which cause a substantial increase of the
electronic effective mass, and high density of states at . The densities
of states of and -plutonium obtained starting from the
open-shell configuration are also in good agreement with the experimental
photoemission spectra.Comment: 6 pages, 3 figure
Effective Hamiltonians for fastly driven many-body lattice systems
We consider 1D lattices described by Hubbard or Bose-Hubbard models, in the
presence of periodic high-frequency perturbations, such as uniform ac force or
modulation of hopping coefficients. Effective Hamiltonians for interacting
particles are derived using an averaging method resembling classical canonical
perturbation theory. As is known, a high-frequency force may renormalize
hopping coefficients, causing interesting phenomena such as coherent
destruction of tunnelling and creation of artificial gauge fields. We find
explicitly additional corrections to the effective Hamiltonians due to
interactions, corresponding to non-trivial processes such as single-particle
density-dependent tunnelling, correlated pair hoppings, nearest neighbour
interactions, etc. Some of these processes arise also in multiband lattice
models, and are capable to give rise to a rich variety of quantum phases. The
apparent contradiction with other methods, e.g. Floquet-Magnus expansion, is
explained. The results may be useful for designing effective Hamiltonian models
in experiments with ultracold atoms, as well as in the field of ultrafast
nonequilibrium magnetism. An example of manipulating exchange interaction in a
Mott-Hubbard insulator is considered, where our corrections play an essential
role
On the phonon-induced superconductivity of disordered alloys
A model of alloy is considered which includes both quenched disorder in the
electron subsystem (``alloy'' subsystem) and electron-phonon interaction. For
given approximate solution for the alloy part of the problem, which is assumed
to be conserving in Baym's sense, we construct the generating functional and
derive the Eliashberg-type equations which are valid to the lowest order in the
adiabatic parameter.The renormalization of bare electron-phonon interaction
vertices by disorder is taken into account consistently with the approximation
for the alloy self-energy. For the case of exact configurational averaging the
same set of equations is established within the usual T-matrix approach. We
demonstrate that for any conserving approximation for the alloy part of the
self-energy the Anderson's theorem holds in the case of isotropic singlet
pairing provided disorder renormalizations of the electron-phonon interaction
vertices are neglected. Taking account of the disorder renormalization of the
electron-phonon interaction we analyze general equations qualitatively and
present the expressions for for the case of weak and intermediate
electron-phonon coupling. Disorder renormalizations of the logarithmic
corrections to the effective coupling, which arise when the effective
interaction kernel for the Cooper channel has the second energy scale, as well
as the renormalization of the dilute paramagnetic impurity suppression are
discussed.Comment: 59 pages, 10 Eps figures, LaTe
Diffraction catastrophes and semiclassical quantum mechanics for Veselago lensing in graphene
We study the effect of trigonal warping on the focussing of electrons by n-p
junctions in graphene. We find that perfect focussing, which was predicted for
massless Dirac fermions, is only preserved for one specific sample orientation.
In the general case, trigonal warping leads to the formation of cusp caustics,
with a different position of the focus for graphene's two valleys. We develop a
semiclassical theory to compute these positions and find very good agreement
with tight-binding simulations. Considering the transmission as a function of
potential strength, we find that trigonal warping splits the single Dirac peak
into two distinct peaks, leading to valley polarization. We obtain the
transmission curves from tight-binding simulations and find that they are in
very good agreement with the results of a billiard model that incorporates
trigonal warping. Furthermore, the positions of the transmission maxima and the
scaling of the peak width are accurately predicted by our semiclassical theory.
Our semiclassical analysis can easily be carried over to other Dirac materials,
which generally have different Fermi surface distortions.Comment: 6 pages, 4 figures, plus supplemental material. Important reference
added and text update
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