1,119 research outputs found
Growth in systems of vesicles and membranes
We present a theoretical study for the intermediate stages of the growth of
membranes and vesicles in supersaturated solutions of amphiphilic molecules.
The problem presents important differences with the growth of droplets in the
classical theory of Lifshitz-Slyozov-Wagner, because the aggregates are
extensive only in two dimensions, but still grow in a three dimensional bath.
The balance between curvature and edge energy favours the nucleation of small
planar membranes, but as they grow beyond a critical size they close themselves
to form vesicles. We obtain a system of coupled equations describing the growth
of planar membranes and vesicles, which is solved numerically for different
initial conditions. Finally, the range of parameters relevant in experimental
situations is discussed.Comment: 13 pages and 5 postscript figures. To appear in Phys. Rev
Dynamics of coherence, localization and excitation transfer in disordered nanorings
Self-assembled supramolecular aggregates are excellent candidates for the
design of efficient excitation transport devices. Both artificially prepared
and natural photosynthetic aggregates in plants and bacteria present an
important degree of disorder that is supposed to hinder excitation transport.
Besides, molecular excitations couple to nuclear motion affecting excitation
transport in a variety of ways. We present an exhaustive study of exciton
dynamics in disordered nanorings with long-range interactions under the
influence of a phonon bath and take the LH2 system of purple bacteria as a
model. Nuclear motion is explicitly taken into account by employing the Davydov
ansatz description of the polaron and quantum dynamics are obtained using a
time-dependent variational method. We reveal an optimal exciton-phonon coupling
that suppresses disorder-induced localization and facilitate excitation
de-trapping. This excitation transfer enhancement, mediated by environmental
phonons, is attributed to energy relaxation toward extended, low-energy
excitons provided by the precise LH2 geometry with anti-parallel dipoles and
long-range interactions. An analysis of localization and spectral statistics is
followed by dynamical measures of coherence and localization, transfer
efficiency and superradiance. Linear absorption, 2D photon-echo spectra and
diffusion measures of the exciton are examined to monitor the diffusive
behavior as a function of the strengths of disorder and exciton-phonon
coupling.Comment: 18 pages, 13 figure
Emergent Symmetry at the N\'eel to Valence-Bond-Solid Transition
We show numerically that the `deconfined' quantum critical point between the
N\'eel antiferromagnet and the columnar valence-bond-solid, for a square
lattice of spin-1/2s, has an emergent symmetry. This symmetry allows
the N\'eel vector and the valence-bond-solid order parameter to be rotated into
each other. It is a remarkable 2+1-dimensional analogue of the symmetry that appears in the scaling limit for the
spin-1/2 Heisenberg chain. The emergent is strong evidence that the
phase transition in the 2+1D system is truly continuous, despite the violations
of finite-size scaling observed previously in this problem. It also implies
surprising relations between correlation functions at the transition. The
symmetry enhancement is expected to apply generally to the critical
two-component Abelian Higgs model (non-compact model). The result
indicates that in three dimensions there is an -symmetric conformal
field theory which has no relevant singlet operators, so is radically different
to conventional Wilson-Fisher-type conformal field theories.Comment: 4+epsilon pages, 6 figure
Effects of many-electron jumps in relaxation and conductivity of Coulomb glasses
A numerical study of the energy relaxation and conductivity of the Coulomb
glass is presented. The role of many-electron transitions is studied by two
complementary methods: a kinetic Monte Carlo algorithm and a master equation in
configuration space method. A calculation of the transition rate for
two-electron transitions is presented, and the proper extension of this to
multi-electron transitions is discussed. It is shown that two-electron
transitions are important in bypassing energy barriers which effectively block
sequential one-electron transitions. The effect of two-electron transitions is
also discussed.Comment: 8 pages, 6 figure
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