701 research outputs found
The equilibrium intrinsic crystal-liquid interface of colloids
We use confocal microscopy to study an equilibrated crystal-liquid interface
in a colloidal suspension. Capillary waves roughen the surface, but locally the
intrinsic interface is sharply defined. We use local measurements of the
structure and dynamics to characterize the intrinsic interface, and different
measurements find slightly different widths of this interface. In terms of the
particle diameter , this width is either (based on structural
information) or (based on dynamics), both not much larger than the
particle size. This work is the first direct experimental visualization of an
equilibrated crystal-liquid interface.Comment: 6 pages; revised version, submitted to PNA
Using mutual information to measure order in model glass-formers
Whether or not there is growing static order accompanying the dynamical
heterogeneity and increasing relaxation times seen in glassy systems is a
matter of dispute. An obstacle to resolving this issue is that the order is
expected to be amorphous and so not amenable to simple order parameters. We use
mutual information to provide a general measurement of order that is sensitive
to multi-particle correlations. We apply this to two glass-forming systems (2D
binary mixtures of hard disks with different size ratios to give varying
amounts of hexatic order) and show that there is little growth of amorphous
order in the system without crystalline order. In both cases we measure the
dynamical length with a four-point correlation function and find that it
increases significantly faster than the static lengths in the system as density
is increased. We further show that we can recover the known scaling of the
dynamic correlation length in a kinetically constrained model, the 2-TLG.Comment: 10 pages, 12 Figure
The Devil is in the details:Pentagonal bipyramids and dynamic arrest
Colloidal suspensions have long been studied as a model for atomic and
molecular systems, due to the ability to fluorescently label and individually
track each particle, yielding particle-resolved structural information. This
allows various local order parameters to be probed that are otherwise
inaccessible for a comparable molecular system. For phase transitions such as
crystallisation, appropriate order parameters which emphasise 6-fold symmetry
are a natural choice, but for vitrification the choice of order parameter is
less clear cut. Previous work has highlighted the importance of icosahedral
local structure as the glass transition is approached. However, counting
icosahedra or related motifs is not a continuous order parameter in the same
way as, for example, the bond-orientational order parameters and .
In this work we investigate the suitability of using pentagonal bipyramid
membership, a structure which can be assembled into larger, five-fold symmetric
structures, as a finer order parameter to investigate the glass transition. We
explore various structural and dynamic properties and show that this new
approach produces many of the same findings as simple icosahedral membership,
but we also find that large instantaneous displacements are often correlated
with significant changes in pentagonal bipyramid membership, and unlike the
population of defective icosahedra, the pentagonal bypyramid membership and
spindle number do not saturate for any measured volume fraction, but continues
to increase.Comment: accepted by JStat Mech: Theory and Experiment 201
On-chip electrically controlled routing of photons from a single quantum dot
Electrical control of on-chip routing of photons emitted by a single InAs/GaAs self-assembled quantum dot (SAQD) is demonstrated in a photonic crystal cavity-waveguide system. The SAQD is located inside an H1 cavity, which is coupled to two photonic crystal waveguides. The SAQD emission wavelength is electrically tunable by the quantum-confined Stark effect. When the SAQD emission is brought into resonance with one of two H1 cavity modes, it is preferentially routed to the waveguide to which that mode is selectively coupled. This proof of concept provides the basis for scalable, low-power, high-speed operation of single-photon routers for use in integrated quantum photonic circuits
Re-entrant melting and freezing in a model system of charged colloids
We studied the phase behavior of charged and sterically stabilized colloids
using confocal microscopy in a less polar solvent (dielectric constant 5.4).
Upon increasing the colloid volume fraction we found a transition from a fluid
to a body centered cubic crystal at 0.0415+/-0.0005, followed by re-entrant
melting at 0.1165+/-0.0015. A second crystal of different symmetry, random
hexagonal close-packed, was formed at a volume fraction around 0.5, similar to
that of hard spheres. We attribute the intriguing phase behavior to particle
interactions that depend strongly on volume fraction, mainly due to changes in
the colloid charge. In this low polarity system the colloids acquire charge
through ion adsorption. The low ionic strength leads to fewer ions per colloid
at elevated volume fractions and consequently a density-dependent colloid
charge.Comment: 25 pages, 5 figures 1 tabl
Colloidal brazil nut effect in sediments of binary charged suspensions
Equilibrium sedimentation density profiles of charged binary colloidal
suspensions are calculated by computer simulations and density functional
theory. For deionized samples, we predict a colloidal ``brazil nut'' effect:
heavy colloidal particles sediment on top of the lighter ones provided that
their mass per charge is smaller than that of the lighter ones. This effect is
verifiable in settling experiments.Comment: 4 pages, 4 figure
Path-dependent initialization of a single quantum dot exciton spin in a nanophotonic waveguide
We demonstrate a scheme for in-plane initialization of a single exciton spin in an InGaAs quantum dot (QD) coupled to a GaAs nanobeam waveguide. The chiral coupling of the QD and the optical mode of the nanobeam enables spin initialization fidelity approaching unity in magnetic field B=1 T and >0.9 without the field. We further show that this in-plane excitation scheme is independent of the incident excitation laser polarization and depends solely on the excitation direction. This scheme provides a robust in-plane spin excitation basis for a photon-mediated spin network for quantum information applications
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