25,609 research outputs found
Projective Quantum Monte Carlo Method for the Anderson Impurity Model and its Application to Dynamical Mean Field Theory
We develop a projective quantum Monte Carlo algorithm of the Hirsch-Fye type
for obtaining ground state properties of the Anderson impurity model. This
method is employed to solve the self-consistency equations of dynamical mean
field theory. It is shown that the approach converges rapidly to the ground
state so that reliable zero-temperature results are obtained. As a first
application, we study the Mott-Hubbard metal-insulator transition of the
one-band Hubbard model, reconfirming the numerical renormalization group
results.Comment: 4 pages, 4 figure
All bicovariant differential calculi on Glq(3,C) and SLq(3,C)
All bicovariant first order differential calculi on the quantum group
GLq(3,C) are determined. There are two distinct one-parameter families of
calculi. In terms of a suitable basis of 1-forms the commutation relations can
be expressed with the help of the R-matrix of GLq(3,C). Some calculi induce
bicovariant differential calculi on SLq(3,C) and on real forms of GLq(3,C). For
generic deformation parameter q there are six calculi on SLq(3,C), on SUq(3)
there are only two. The classical limit q-->1 of bicovariant calculi on
SLq(3,C) is not the ordinary calculus on SL(3,C). One obtains a deformation of
it which involves the Cartan-Killing metric.Comment: 24 pages, LaTe
Non-monotonous crossover between capillary condensation and interface localisation/delocalisation transition in binary polymer blends
Within self-consistent field theory we study the phase behaviour of a
symmetric binary AB polymer blend confined into a thin film. The film surfaces
interact with the monomers via short range potentials. One surface attracts the
A component and the corresponding semi-infinite system exhibits a first order
wetting transition. The surface interaction of the opposite surface is varied
as to study the crossover from capillary condensation for symmetric surface
fields to the interface localisation/delocalisation transition for
antisymmetric surface fields. In the former case the phase diagram has a single
critical point close to the bulk critical point. In the latter case the phase
diagram exhibits two critical points which correspond to the prewetting
critical points of the semi-infinite system. The crossover between these
qualitatively different limiting behaviours occurs gradually, however, the
critical temperature and the critical composition exhibit a non-monotonic
dependence on the surface field.Comment: to appear in Europhys.Let
Intrinsic profiles and capillary waves at homopolymer interfaces: a Monte Carlo study
A popular concept which describes the structure of polymer interfaces by
``intrinsic profiles'' centered around a two dimensional surface, the ``local
interface position'', is tested by extensive Monte Carlo simulations of
interfaces between demixed homopolymer phases in symmetric binary (AB)
homopolymer blends, using the bond fluctuation model. The simulations are done
in an LxLxD geometry. The interface is forced to run parallel to the LxL planes
by imposing periodic boundary conditions in these directions and fixed boundary
conditions in the D direction, with one side favoring A and the other side
favoring B. Intrinsic profiles are calculated as a function of the ``coarse
graining length'' B by splitting the system into columns of size BxBxD and
averaging in each column over profiles relative to the local interface
position. The results are compared to predictions of the self-consistent field
theory. It is shown that the coarse graining length can be chosen such that the
interfacial width matches that of the self-consistent field profiles, and that
for this choice of B the ``intrinsic'' profiles compare well with the
theoretical predictions.Comment: to appear in Phys. Rev.
The Keck/OSIRIS Nearby AGN Survey (KONA) I. The Nuclear K-band Properties of Nearby AGN
We introduce the Keck Osiris Nearby AGN survey (KONA), a new adaptive
optics-assisted integral-field spectroscopic survey of Seyfert galaxies. KONA
permits at ~0.1" resolution a detailed study of the nuclear kinematic structure
of gas and stars in a representative sample of 40 local bona fide active
galactic nucleus (AGN). KONA seeks to characterize the physical processes
responsible for the coevolution of supermassive black holes and galaxies,
principally inflows and outflows. With these IFU data of the nuclear regions of
40 Seyfert galaxies, the KONA survey will be able to study, for the first time,
a number of key topics with meaningful statistics. In this paper we study the
nuclear K-band properties of nearby AGN. We find that the luminosities of the
unresolved Seyfert 1 sources at 2.1 microns are correlated with the hard X-ray
luminosities, implying that the majority of the emission is non-stellar. The
best-fit correlation is logLK = 0.9logL2-10 keV + 4 over 3 orders of magnitude
in both K-band and X-ray luminosities. We find no strong correlation between
2.1 microns luminosity and hard X-ray luminosity for the Seyfert 2 galaxies.
The spatial extent and spectral slope of the Seyfert 2 galaxies indicate the
presence of nuclear star formation and attenuating material (gas and dust),
which in some cases is compact and in some galaxies extended. We detect
coronal-line emission in 36 galaxies and for the first time in five galaxies.
Finally, we find 4/20 galaxies that are optically classified as Seyfert 2 show
broad emission lines in the near-IR, and one galaxy (NGC 7465) shows evidence
of a double nucleus.Comment: Accepted for publication in ApJ, 19 pages with 18 figure
Iterative Perturbation Theory for Strongly Correlated Electron Systems with Orbital Degeneracy
A new scheme of the iterative perturbation theory is proposed for the
strongly correlated electron systems with orbital degeneracy. The method is
based on the modified self-energy of Yeyati, et al. which interpolates between
the weak and the strong correlation limits, but a much simpler scheme is
proposed which is useful in the case of the strong correlation with orbital
degeneracy. It will be also useful in the study of the electronic structures
combined with the band calculations.Comment: 6 pages, 3 Postscript figures, to appear in J. Phys. Cond. Matte
Building block libraries and structural considerations in the self-assembly of polyoxometalate and polyoxothiometalate systems
Inorganic metal-oxide clusters form a class of compounds that are unique in their topological and electronic versatility and are becoming increasingly more important in a variety of applications. Namely, Polyoxometalates (POMs) have shown an unmatched range of physical properties and the ability to form structures that can bridge several length scales. The formation of these molecular clusters is often ambiguous and is governed by self-assembly processes that limit our ability to rationally design such molecules. However, recent years have shown that by considering new building block principles the design and discovery of novel complex clusters is aiding our understanding of this process. Now with current progress in thiometalate chemistry, specifically polyoxothiometalates (POTM), the field of inorganic molecular clusters has further diversified allowing for the targeted development of molecules with specific functionality. This chapter discusses the main differences between POM and POTM systems and how this affects synthetic methodologies and reactivities. We will illustrate how careful structural considerations can lead to the generation of novel building blocks and further deepen our understanding of complex systems
Orbital selective insulator-metal transition in V2O3 under external pressure
We present a detailed account of the physics of Vanadium sesquioxide (), a benchmark system for studying correlation induced metal-insulator
transition(s). Based on a detailed perusal of a wide range of experimental
data, we stress the importance of multi-orbital Coulomb interactions in concert
with first-principles LDA bandstructure for a consistent understanding of the
PI-PM MIT under pressure. Using LDA+DMFT, we show how the MIT is of the orbital
selective type, driven by large changes in dynamical spectral weight in
response to small changes in trigonal field splitting under pressure. Very good
quantitative agreement with () the switch of orbital occupation and ()
S=1 at each site across the MIT, and () carrier effective mass in
the PM phase, is obtained. Finally, using the LDA+DMFT solution, we have
estimated screening induced renormalisation of the local, multi-orbital Coulomb
interactions. Computation of the one-particle spectral function using these
screened values is shown to be in excellent quantitative agreement with very
recent experimental (PES and XAS) results. These findings provide strong
support for an orbital-selective Mott transition in paramagnetic .Comment: 12 pages, 7 figure
Random RNA under tension
The Laessig-Wiese (LW) field theory for the freezing transition of random RNA
secondary structures is generalized to the situation of an external force. We
find a second-order phase transition at a critical applied force f = f_c. For f
f_c, the extension L as a function of
pulling force f scales as (f-f_c)^(1/gamma-1). The exponent gamma is calculated
in an epsilon-expansion: At 1-loop order gamma = epsilon/2 = 1/2, equivalent to
the disorder-free case. 2-loop results yielding gamma = 0.6 are briefly
mentioned. Using a locking argument, we speculate that this result extends to
the strong-disorder phase.Comment: 6 pages, 10 figures. v2: corrected typos, discussion on locking
argument improve
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