4,977 research outputs found
Hypersonic laminar boundary layers around slender bodies
Compressible laminar boundary layer equations considered for hypersonic flow around slender bodie
Boundary conditions and defect lines in the Abelian sandpile model
We add a defect line of dissipation, or crack, to the Abelian sandpile model.
We find that the defect line renormalizes to separate the two-dimensional plane
into two half planes with open boundary conditions. We also show that varying
the amount of dissipation at a boundary of the Abelian sandpile model does not
affect the universality class of the boundary condition. We demonstrate that a
universal coefficient associated with height probabilities near the defect can
be used to classify boundary conditions.Comment: 8 pages, 1 figure; suggestions from referees incorporated; to be
published in Phys. Rev.
Vacancy localization in the square dimer model
We study the classical dimer model on a square lattice with a single vacancy
by developing a graph-theoretic classification of the set of all configurations
which extends the spanning tree formulation of close-packed dimers. With this
formalism, we can address the question of the possible motion of the vacancy
induced by dimer slidings. We find a probability 57/4-10Sqrt[2] for the vacancy
to be strictly jammed in an infinite system. More generally, the size
distribution of the domain accessible to the vacancy is characterized by a
power law decay with exponent 9/8. On a finite system, the probability that a
vacancy in the bulk can reach the boundary falls off as a power law of the
system size with exponent 1/4. The resultant weak localization of vacancies
still allows for unbounded diffusion, characterized by a diffusion exponent
that we relate to that of diffusion on spanning trees. We also implement
numerical simulations of the model with both free and periodic boundary
conditions.Comment: 35 pages, 24 figures. Improved version with one added figure (figure
9), a shift s->s+1 in the definition of the tree size, and minor correction
Mott-Kondo Insulator Behavior in the Iron Oxychalcogenides
We perform a combined experimental-theoretical study of the
Fe-oxychalcogenides (FeO\emph{Ch}) series
LaOFeO\emph{M} (\emph{M}=S, Se), which is the latest
among the Fe-based materials with the potential \ to show unconventional
high-T superconductivity (HTSC). A combination of incoherent Hubbard
features in X-ray absorption (XAS) and resonant inelastic X-ray scattering
(RIXS) spectra, as well as resitivity data, reveal that the parent
FeO\emph{Ch} are correlation-driven insulators. To uncover microscopics
underlying these findings, we perform local density
approximation-plus-dynamical mean field theory (LDA+DMFT) calculations that
unravel a Mott-Kondo insulating state. Based upon good agreement between theory
and a range of data, we propose that FeO\emph{Ch} may constitute a new, ideal
testing ground to explore HTSC arising from a strange metal proximate to a
novel selective-Mott quantum criticality
Selective interlayer ferromagnetic coupling between the Cu spins in YBa Cu O grown on top of La Ca MnO
Studies to date on ferromagnet/d-wave superconductor heterostructures focus
mainly on the effects at or near the interfaces while the response of bulk
properties to heterostructuring is overlooked. Here we use resonant soft x-ray
scattering spectroscopy to reveal a novel c-axis ferromagnetic coupling between
the in-plane Cu spins in YBa Cu O (YBCO) superconductor when it
is grown on top of ferromagnetic La Ca MnO (LCMO) manganite
layer. This coupling, present in both normal and superconducting states of
YBCO, is sensitive to the interfacial termination such that it is only observed
in bilayers with MnO_2but not with La Ca interfacial
termination. Such contrasting behaviors, we propose, are due to distinct
energetic of CuO chain and CuO plane at the La Ca and
MnO terminated interfaces respectively, therefore influencing the transfer
of spin-polarized electrons from manganite to cuprate differently. Our findings
suggest that the superconducting/ferromagnetic bilayers with proper interfacial
engineering can be good candidates for searching the theorized
Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in cuprates and studying the
competing quantum orders in highly correlated electron systems.Comment: Please note the change of the title. Text might be slightly different
from the published versio
Topological Surface States and Dirac point tuning in ternary Bi2Te2Se class of topological insulators
Using angle-resolved photoemission spectroscopy, we report electronic
structure for representative members of ternary topological insulators. We show
that several members of this family, such as Bi2Se2Te, Bi2Te2Se, and GeBi2Te4,
exhibit a singly degenerate Dirac-like surface state, while Bi2Se2S is a fully
gapped insulator with no measurable surface state. One of these compounds,
Bi2Se2Te, shows tunable surface state dispersion upon its electronic alloying
with Sb (SbxBi2-xSe2Te series). Other members of the ternary family such as
GeBi2Te4 and BiTe1.5S1.5 show an in-gap surface Dirac point, the former of
which has been predicted to show nonzero weak topological invariants such as
(1;111); thus belonging to a different topological class than BiTe1.5S1.5. The
measured band structure presented here will be a valuable guide for
interpreting transport, thermoelectric, and thermopower measurements on these
compounds. The unique surface band topology observed in these compounds
contributes towards identifying designer materials with desired flexibility
needed for thermoelectric and spintronic device fabrication.Comment: 9 pages, 6 figures; Related results at
http://online.kitp.ucsb.edu/online/topomat11/hasan
Height variables in the Abelian sandpile model: scaling fields and correlations
We compute the lattice 1-site probabilities, on the upper half-plane, of the
four height variables in the two-dimensional Abelian sandpile model. We find
their exact scaling form when the insertion point is far from the boundary, and
when the boundary is either open or closed. Comparing with the predictions of a
logarithmic conformal theory with central charge c=-2, we find a full
compatibility with the following field assignments: the heights 2, 3 and 4
behave like (an unusual realization of) the logarithmic partner of a primary
field with scaling dimension 2, the primary field itself being associated with
the height 1 variable. Finite size corrections are also computed and
successfully compared with numerical simulations. Relying on these field
assignments, we formulate a conjecture for the scaling form of the lattice
2-point correlations of the height variables on the plane, which remain as yet
unknown. The way conformal invariance is realized in this system points to a
local field theory with c=-2 which is different from the triplet theory.Comment: 68 pages, 17 figures; v2: published version (minor corrections, one
comment added
Surface electronic structure of a topological Kondo insulator candidate SmB6: insights from high-resolution ARPES
The Kondo insulator SmB6 has long been known to exhibit low temperature (T <
10K) transport anomaly and has recently attracted attention as a new
topological insulator candidate. By combining low-temperature and high
energy-momentum resolution of the laser-based ARPES technique, for the first
time, we probe the surface electronic structure of the anomalous conductivity
regime. We observe that the bulk bands exhibit a Kondo gap of 14 meV and
identify in-gap low-lying states within a 4 meV window of the Fermi level on
the (001)-surface of this material. The low-lying states are found to form
electron-like Fermi surface pockets that enclose the X and the Gamma points of
the surface Brillouin zone. These states disappear as temperature is raised
above 15K in correspondence with the complete disappearance of the 2D
conductivity channels in SmB6. While the topological nature of the in-gap
metallic states cannot be ascertained without spin (spin-texture) measurements
our bulk and surface measurements carried out in the
transport-anomaly-temperature regime (T < 10K) are consistent with the
first-principle predicted Fermi surface behavior of a topological Kondo
insulator phase in this material.Comment: 4 Figures, 6 Page
Abelian Sandpile Model on the Honeycomb Lattice
We check the universality properties of the two-dimensional Abelian sandpile
model by computing some of its properties on the honeycomb lattice. Exact
expressions for unit height correlation functions in presence of boundaries and
for different boundary conditions are derived. Also, we study the statistics of
the boundaries of avalanche waves by using the theory of SLE and suggest that
these curves are conformally invariant and described by SLE2.Comment: 24 pages, 5 figure
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