62 research outputs found
Adaptively truncated Hilbert space based impurity solver for dynamical mean-field theory
We present an impurity solver based on adaptively truncated Hilbert spaces.
The solver is particularly suitable for dynamical mean-field theory in
circumstances where quantum Monte Carlo approaches are ineffective. It exploits
the sparsity structure of quantum impurity models, in which the interactions
couple only a small subset of the degrees of freedom. We further introduce an
adaptive truncation of the particle or hole excited spaces, which enables
computations of Green functions with an accuracy needed to avoid unphysical
(sign change of imaginary part) self-energies. The method is benchmarked on the
one-dimensional Hubbard model.Comment: 10 pages, 7 figure
Pyrochlore electrons under pressure, heat and field: shedding light on the iridates
We study the finite temperature and magnetic field phase diagram of electrons
on the pyrochlore lattice subject to a local repulsion as a model for the
pyrochlore iridates. We provide the most general symmetry-allowed Hamiltonian,
including next-nearest neighbour hopping, and relate it to a Slater-Koster
based Hamiltonian for the iridates. It captures Lifshitz and/or thermal
transitions between several phases such as metals, semimetals, topological
insulators and Weyl semimetals, and gapped antiferromagnets with different
orders. Our results on the charge conductivity, both DC and optical, Hall
coefficient, magnetization and susceptibility show good agreement with recent
experiments and provide new predictions. As such, our effective model sheds
light on the pyrochlore iridates in a unified way.Comment: 6+3 pages, 7+2 figures. v3: expanded version, with 3 new figure
Properties of the one-dimensional Hubbard model: cellular dynamical mean-field description
The one-dimensional half-filled Hubbard model is considered at zero
temperature within the cellular dynamical mean-field theory (CDMFT). By the
computation of the spectral gap and the energy density with various cluster and
bath sizes we examine the accuracy of the CDMFT in a systematic way, which
proves the accurate description of the one-dimensional systems by the CDMFT
with small clusters. We also calculate the spectral weights in a full range of
the momentum for various interaction strengths. The results do not only account
for the spin-charge separation, but they also reproduce all the features of the
Bethe ansatz dispersions, implying that the CDMFT provides an excellent
description of the spectral properties of low-dimensional interacting systems.Comment: J. Phys.: Condens. Matter, in pres
The role of alpha and beta adrenergic receptors in cortisol-induced hyperglycaemia in the common African toad (Bufo regularis)
The role of adrenergic receptors in cortisol-induced hyperglycaemia is not well known. The present study investigates the effects of adrenergic receptor blockers in cortisol-induced hyperglycaemia in the common African toad (Bufo regularis). Each toad was fasted and anesthetized with sodium pentobarbitone (3 mg/100 g i.p). The animals (control) received intravenous (i.v) injection of 0.7% amphibian saline while animals (untreated) were given cortisol (20 μg/kg). In pre-treatment groups, animals received prazosin (0.2 mg/kg i.v), propranolol 0.5 mg/kg or combination of prazosin (0.2 mg/kg i.v) and propranolol (0.5 mg/kg i.v) before i.v injection of cortisol (20 μg/kg). Thereafter, blood samples were collected for estimation of blood glucose level using the modified glucose oxidase method. Cortisol caused significant increase in blood glucose level from 44.4±3.8 to 71.7±9.7 mg/dl. Pretreatment of the toads with propranolol (0.5 mg/kg i.v) caused significant reduction (p≤ 0.01) in cortisolinduced hyperglycaemia while pre-treatment with prazosin (0.2 mg/kg i.v) produced no significant effect on hyperglycaemia induced by cortisol. The combination of both prazosin and propranolol completely abolished the effects of cortisol on blood glucose level. The results suggest that cortisol-induced hyperglycaemia in the toad (B. regularis) is mediated probably by both the α- and β-adrenergic receptors with the beta adrenergic receptors playing dominant role.Keywords: Cortisol, hyperglycaemia, prazosin, propranolol, amphibian saline, common African toad.African Journal of Biotechnology Vol. 12(36), pp. 5554-555
Imaginary-time matrix product state impurity solver for dynamical mean-field theory
We present a new impurity solver for dynamical mean-field theory based on
imaginary-time evolution of matrix product states. This converges the
self-consistency loop on the imaginary-frequency axis and obtains
real-frequency information in a final real-time evolution. Relative to
computations on the real-frequency axis, required bath sizes are much smaller
and less entanglement is generated, so much larger systems can be studied. The
power of the method is demonstrated by solutions of a three band model in the
single and two-site dynamical mean-field approximation. Technical issues are
discussed, including details of the method, efficiency as compared to other
matrix product state based impurity solvers, bath construction and its relation
to real-frequency computations and the analytic continuation problem of quantum
Monte Carlo, the choice of basis in dynamical cluster approximation, and
perspectives for off-diagonal hybridization functions.Comment: 8 pages + 4 pages appendix, 9 figure
Emergent localized states at the interface of a twofold -symmetric lattice
We consider the role of non-triviality resulting from a non-Hermitian
Hamiltonian that conserves twofold PT-symmetry assembled by interconnections
between a PT-symmetric lattice and its time reversal partner. Twofold
PT-symmetry in the lattice produces additional surface exceptional points that
play the role of new critical points, along with the bulk exceptional point. We
show that there are two distinct regimes possessing symmetry-protected
localized states, of which localization lengths are robust against external
gain and loss. The states are demonstrated by numerical calculation of a
quasi-1D ladder lattice and a 2D bilayered square lattice.Comment: 10 pages, 7 figure
Influence of nitric oxide on histamine and carbachol – induced gastric acid secretion in the common African toad – Bufo regularis
The study aimed to determine the influence of nitric oxide (NO) on the action of histamine and carbachol on acid secretion in the common African toad – Bufo regularis. Gastric acidity was determined by titration method. The acid secretion was determined when nitric oxide was absent following administration of NO synthase inhibitor; N-nitro-L-arginine methyl ester (L-NAME) and when nitric oxide was in excess by administration of exogenous NO donor, sodium nitroprusside (SNP). Histamine or carbachol increased acid secretion in the toad. Acid output increased from 0.32 ± 0.04 mEq/15min to 0.56 ± 0.08 and 0.61 ± 0.05 mEq/15min for histamine and carbachol respectively (P < 0.05). Pretreatment of the toad with L-NAME produced further increases in histamine (0.62 ± 0.06 mEq/15min) or carbachol (0.74 ± 0.06 mEq/15min) induced acid secretion respectively. SNP however, completely abolished the acid secretion stimulated by either histamine or carbachol. It was therefore concluded that nitric oxide has a negative influence on the histamine or carbachol – stimulated acid secretion in the toad – Bufo regularis.Keywords: nitric oxide, histamine, carbachol, acid secretion Nigerian Journal of Physiological Sciences Vol. 20(1&2) 2005: 74-7
Interplay between spin-orbit coupling and van Hove singularity in the Hund's metallicity of SrRuO
We investigate the dynamical properties of SrRuO at zero and very low
temperature using density functional theory plus dynamical mean-field theory
with an exact diagonalization solver. By considering rotationally invariant
local interaction, we examine how Hund's coupling and spin-orbit coupling
affect the correlated nature of the system. In the absence of Hund's coupling,
the system shows a Fermi liquid behavior over the entire range of temperatures
we consider. We confirm that the Fermi liquid persists at zero temperature even
with nonzero Hund's coupling; however, at sufficient temperatures Hund's
coupling significantly reduces the Fermi liquid regime and the system evolves
into a typical Hund's metal. At the bare electronic occupancy of SrRuO
(), a stronger Hund's metallicity accompanies a larger long-time
correlator. Remarkably, electron doping further destabilizes the Fermi liquid
even though the long-time correlator and magnetic fluctuations decrease upon
doping. This suppression of the Fermi liquid is driven by the van Hove
singularity above the Fermi level in SrRuO, combined with an enhanced
Van Vleck susceptibility by spin-orbit coupling. Such findings point to the
important role that electronic structure plays in the behavior of Hund's
metals, in addition to magnetic fluctuations.Comment: 7 pages, 4 figure
- …