57,405 research outputs found
Structural and dynamical features of multiple metastable glassy states in a colloidal system with competing interactions
Systems in which a short-ranged attraction and long-ranged repulsion compete
are intrinsically frustrated, leading their structure and dynamics to be
dominated either by mesoscopic order or by metastable disorder. Here we report
the latter case in a colloidal system with long-ranged electrostatic repulsions
and short-ranged depletion attractions. We find a variety of states exhibiting
slow non-diffusive dynamics: a gel, a glassy state of clusters, and a state
reminiscent of a Wigner glass. Varying the interactions, we find a continuous
crossover between the Wigner and cluster glassy states, and a sharp
discontinuous transition between the Wigner glassy state and gel. This
difference reflects the fact that dynamic arrest is driven by repulsion for the
two glassy states and attraction in the case of the gel
Interference Effects on Kondo-Assisted Transport through Double Quantum Dots
We systematically investigate electron transport through double quantum dots
with particular emphasis on interference induced via multiple paths of electron
propagation. By means of the slave-boson mean-field approximation, we calculate
the conductance, the local density of states, the transmission probability in
the Kondo regime at zero temperature. It is clarified how the Kondo-assisted
transport changes its properties when the system is continuously changed among
the serial, parallel and T-shaped double dots. The obtained results for the
conductance are explained in terms of the Kondo resonances influenced by
interference effects. We also discuss the impacts due to the spin-polarization
of ferromagnetic leads.Comment: 9 pages, 11 figures ; minor corrections and references adde
Existence of Different Intermediate Hamiltonians in Type A N-fold Supersymmetry
Type A N-fold supercharge admits a one-parameter family of factorizations
into product of N first-order linear differential operators due to an
underlying GL(2,C) symmetry. As a consequence, a type A N-fold supersymmetric
system can have different intermediate Hamiltonians corresponding to different
factorizations. We derive the necessary and sufficient conditions for the
latter system to possess intermediate Hamiltonians for the N=2 case. We then
show that whenever it has (at least) one intermediate Hamiltonian, it can admit
second-order parasupersymmetry and a generalized 2-fold superalgebra. As an
illustration, we construct a set of generalized Poeschl--Teller potentials of
this kind.Comment: 17 pages, no figures; minor corrections, to appear in Annals of
Physic
The interplay of sedimentation and crystallization in hard-sphere suspensions
We study crystal nucleation under the influence of sedimentation in a model
of colloidal hard spheres via Brownian Dynamics simulations. We introduce two
external fields acting on the colloidal fluid: a uniform gravitational field
(body force), and a surface field imposed by pinning a layer of equilibrium
particles (rough wall). We show that crystal nucleation is suppressed in
proximity of the wall due to the slowing down of the dynamics, and that the
spatial range of this effect is governed by the static length scale of bond
orientational order. For distances from the wall larger than this length scale,
the nucleation rate is greatly enhanced by the process of sedimentation, since
it leads to a higher volume fraction, or a higher degree of supercooling, near
the bottom. The nucleation stage is similar to the homogeneous case, with
nuclei being on average spherical and having crystalline planes randomly
oriented in space. The growth stage is instead greatly affected by the symmetry
breaking introduced by the gravitation field, with a slowing down of the
attachment rate due to density gradients, which in turn cause nuclei to grow
faster laterally. Our findings suggest that the increase of crystal nucleation
in higher density regions might be the cause of the large discrepancy in the
crystal nucleation rate of hard spheres between experiments and simulations, on
noting that the gravitational effects in previous experiments are not
negligible.Comment: 16 pages, 15 figures, 2 tables; Soft Matter (2013
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