105 research outputs found
Quantifying hidden order out of equilibrium
While the equilibrium properties, states, and phase transitions of
interacting systems are well described by statistical mechanics, the lack of
suitable state parameters has hindered the understanding of non-equilibrium
phenomena in diverse settings, from glasses to driven systems to biology. The
length of a losslessly compressed data file is a direct measure of its
information content: The more ordered the data is, the lower its information
content and the shorter the length of its encoding can be made. Here, we
describe how data compression enables the quantification of order in
non-equilibrium and equilibrium many-body systems, both discrete and
continuous, even when the underlying form of order is unknown. We consider
absorbing state models on and off-lattice, as well as a system of active
Brownian particles undergoing motility-induced phase separation. The technique
reliably identifies non-equilibrium phase transitions, determines their
character, quantitatively predicts certain critical exponents without prior
knowledge of the order parameters, and reveals previously unknown ordering
phenomena. This technique should provide a quantitative measure of organization
in condensed matter and other systems exhibiting collective phase transitions
in and out of equilibrium
Binodal Colloidal Aggregation Test - 4: Polydispersion
Binodal Colloidal Aggregation Test - 4: Polydispersion (BCAT-4-Poly) will use model hard-spheres to explore seeded colloidal crystal nucleation and the effects of polydispersity, providing insight into how nature brings order out of disorder. Crewmembers photograph samples of polymer and colloidal particles (tiny nanoscale spheres suspended in liquid) that model liquid/gas phase changes. Results will help scientists develop fundamental physics concepts previously cloaked by the effects of gravity
Peak Effect in Superconductors: Melting of Larkin Domains
Motivated by the recent observations of the peak effect in high- YBCO
superconductors, we reexamine the origin of this unusual phenomenon. We show
that the mechanism based on the -dependence (nonlocality) of the
vortex-lattice tilt modulus cannot account for the essential
feature of the peak effect. We propose a scenario in which the peak effect is
related to the melting of Larkin domains. In our model, the rise of critical
current with increasing temperature is a result of a crossover from the Larkin
pinning length to the length scale set by thermally excited free dislocations.Comment: 13 pages, 2 figures, REVTE
Binary Colloidal Alloy Test-5: Aspheres
The Binary Colloidal Alloy Test - 5: Aspheres (BCAT-5-Aspheres) experiment photographs initially randomized colloidal samples (tiny nanoscale spheres suspended in liquid) in microgravity to determine their resulting structure over time. BCAT-5-Aspheres will study the properties of concentrated systems of small particles when they are identical, but not spherical in microgravity.
Quantum Phase Transition in Heisenberg-Kitaev Model
We explore the nature of the quantum phase transition between a magnetically
ordered state with collinear spin pattern and a gapless spin liquid in
the Heisenberg-Kitaev model. We construct a slave particle mean field theory
for the Heisenberg-Kitaev model in terms of complex fermionic spinons. It is
shown that this theory, formulated in the appropriate basis, is capable of
describing the Kitaev spin liquid as well as the transition between the gapless
spin liquid and the so-called stripy antiferromagnet. In particular,
within a mean field theory, we have a discontinuous transition from the
spin liquid to the stripy antiferromagnet. We argue, however, that subtle
spinon confinement effects, associated with the instability of gapped U(1) spin
liquid in two spatial dimensions, are playing an important role at the
transition. The possibility of an exotic continuous transition is briefly
addressed.Comment: 12 pages, 6 figure
Isotropic Band Gaps and Freeform Waveguides Observed in Hyperuniform Disordered Photonic Solids
Recently, disordered photonic media and random textured surfaces have
attracted increasing attention as strong light diffusers with broadband and
wide-angle properties. We report the first experimental realization of an
isotropic complete photonic band gap (PBG) in a two-dimensional (2D) disordered
dielectric structure. This structure is designed by a constrained-optimization
method, which combines advantages of both isotropy due to disorder and
controlled scattering properties due to low density fluctuations
(hyperuniformity) and uniform local topology. Our experiments use a modular
design composed of Al2O3 walls and cylinders arranged in a hyperuniform
disordered network. We observe a complete PBG in the microwave region, in good
agreement with theoretical simulations, and show that the intrinsic isotropy of
this novel class of PBG materials enables remarkable design freedom, including
the realization of waveguides with arbitrary bending angles impossible in
photonic crystals. This first experimental verification of a complete PBG and
realization of functional defects in this new class of materials demonstrates
their potential as building blocks for precise manipulation of photons in
planar optical micro-circuits and has implications for disordered acoustic and
electronic bandgap materials
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