35 research outputs found
Consistent partial bosonization of the extended Hubbard model
We design an efficient and balanced approach that captures major effects of collective electronic fluctuations in strongly correlated fermionic systems using a simple diagrammatic expansion on a basis of dynamical mean-field theory. For this aim we perform a partial bosonization of collective fermionic fluctuations in leading channels of instability. We show that a simultaneous account for different bosonic channels can be done in a consistent way that allows to avoid the famous Fierz ambiguity problem. The present method significantly improves a description of an effective screened interaction W in both charge and spin channels, and has a great potential for application to realistic GW-like calculations for magnetic materials. © 2019 American Physical Society
Impact of partially bosonized collective fluctuations on electronic degrees of freedom
In this work we present a comprehensive analysis of collective electronic
fluctuations and their effect on single-particle properties of the Hubbard
model. Our approach is based on a standard dual fermion/boson scheme with the
interaction truncated at the two-particle level. Within this framework we
compare various approximations that differ in the set of diagrams (ladder vs
exact diagrammatic Monte Carlo), and/or in the form of the four-point
interaction vertex (exact vs partially bosonized). This allows to evaluate the
effect of all components of the four-point vertex function on the electronic
self-energy. In particular, we observe that contributions that are not
accounted for by the partially bosonized approximation for the vertex have only
a minor effect on electronic degrees of freedom in a broad range of model
parameters. In addition, we find that in the regime, where the ladder dual
fermion approximation provides an accurate solution of the problem, the leading
contribution to the self-energy is given by the longitudional bosonic modes.
This can be explained by the fact that contributions of transverse
particle-hole and particle-particle modes partially cancel each other. Our
results justify the applicability of the recently introduced dual triply
irreducible local expansion (D-TRILEX) method that represents one of the
simplest consistent diagrammatic extensions of the dynamical mean-field theory.
We find that the self-consistent D-TRILEX approach is reasonably accurate also
in challenging regimes of the Hubbard model, even where the dynamical
mean-field theory does not provide the optimal local reference point (impurity
problem) for the diagrammatic expansion
Multi-band D-TRILEX approach to materials with strong electronic correlations
We present the multi-band dual triply irreducible local expansion (D-TRILEX) approach to interacting electronic systems and discuss its numerical implementation. This method is designed for a self-consistent description of multi-orbital systems that can also have several atoms in the unit cell. The current implementation of the D-TRILEX approach is able to account for the frequency- and channel-dependent long-ranged electronic interactions. We show that our method is accurate when applied to small multi-band systems such as the Hubbard-Kanamori dimer. Calculations for the extended Hubbard, the two-orbital Hubbard-Kanamori, and the bilayer Hubbard models are also discussed
Extended regime of coexisting metallic and insulating phases in a two-orbital electronic system
We investigate the metal-to-insulator phase transition driven by electronic
interactions in the quarter-filled Hubbard-Kanamori model on a cubic lattice
with two orbitals split by a crystal field. We show that a systematic
consideration of the non-local collective electronic fluctuations strongly
affects the state-of-the-art picture of the phase transition provided by the
dynamical mean field theory. Our calculations reveal a region of phase
coexistence between the metallic and the Mott insulating states, which is
missing in the local approximation to electronic correlations. This coexistence
region is remarkably broad in terms of the interaction strength. It starts at a
critical value of the interaction slightly larger than the bandwidth and
extends to more than twice the bandwidth, where the two solutions merge into a
Mott insulating phase. Our results illustrate that non-local correlations can
have crucial consequences on the electronic properties in the strongly
correlated regime, even in the simplest multi-orbital systems
Coexisting charge density wave and ferromagnetic instabilities in monolayer InSe
Recently fabricated InSe monolayers exhibit remarkable characteristics that
indicate the potential of this material to host a number of many-body
phenomena. Here, we consistently describe collective electronic effects in
hole-doped InSe monolayers using advanced many-body techniques. To this end, we
derive a realistic electronic-structure model from first principles that takes
into account the most important characteristics of this material, including a
flat band with prominent van Hove singularities in the electronic spectrum,
strong electron-phonon coupling, and weakly-screened long-ranged Coulomb
interactions. We calculate the temperature-dependent phase diagram as a
function of band filling and observe that this system is in a regime with
coexisting charge density wave and ferromagnetic instabilities that are driven
by strong electronic Coulomb correlations. This regime can be achieved at
realistic doping levels and high enough temperatures, and can be verified
experimentally. We find that the electron-phonon interaction does not play a
crucial role in these effects, effectively suppressing the local Coulomb
interaction without changing the qualitative physical picture
STUDY OF CYLPEBS CHILLING
Methods of increasing the shock resistance of cast-iron grinding bodies are researched. The models of heat transfer in the process of casting and shock-abrasive wear are presented. Tooling to produce experimental samples of milling bodies chilling(gravity die casting) is manufactured, samples of cylpebs are produced
СЛУЧАЙ МИОПАТИИ ЭРБА-РОТА
The article presents a clinical case of a patient with Erb-Roth’s hereditary neuromuscular dystrophy presented with severe cardiomyopathy.В статье представлен клинический случай развития тяжелой формы кардиомиопатии у пациента, страдающего наследственным нейромышечным заболеванием – миопатией Эрба-Рота