arXiv subjects

N. I. Chashchin

Publications and source records attributed to N. I. Chashchin.

4 recordsLinked to original sources

arXiv2024

Quantum Phase Transitions in 2D--dimensional paramagnetic half--filled Hubbard model

We investigate the quantum phase transitions in strongly correlated electronic systems at $T=0^0K$ by the example of the 2D Hubbard model. The model for numerical calculations were formalized in terms of the integral equations previously obtained for the half--filled paramagnetic Hubbard model by means of the variational derivatives technique and subsequent Legendre transformation. For principal results we submit in series the momentum distribution functions $n(k)$ which display distinct attributes for the incipient regimes: the pure doublon phase, the metal phase, Weyl semimetal phase, and Weyl excitonic insulator phase at the sequential increasing the onsite Coulomb interaction $U$.

cond-mat.str-el↗

arXiv2020

Localized excitons in 1D half-filled paramagnetic Hubbard model

By the example of the Hubbard model we analytically and numerically examine the formating and coexisting of localized electron--electron pairs (doublons) and localized electron--hole pairs (Frenkel--type excitons) . Here we demonstrate that at a variation of the on-site Coulomb repulsion U there occurs a quantum transition from the doublon to the exciton regime that is conditioned by the low-energy effective hybridization of the valence and conductivity subbands. We calculate momentum distribution functions and electronic spectrum functions for different U, which reveal topologically nontrivial behaviour at the Fermi level.

cond-mat.str-el↗

arXiv2018

D--dimensional half--filled Hubbard model. Zero temperature paramagnetic solution

In this paper we investigate effects of a lattice dimension on strongly correlated electronic systems at $T=0 K$. The model for numerical calculations is formalized in terms of the integral equations which were obtained previously for the half -- filled paramagnetic Hubbard model. The assumption that all relevant functions of the system have a magnitude dependence of momentus vectors makes ultimately possible treating a lattice dimension $D$ as an external parameter. We here submit for consideration the number of doubly occupied lattice sites, the electronic density of states, and the momentum distribution in electronic occupation numbers at $D$=1, $D$=2, $D$=3

cond-mat.str-el↗

arXiv2017

1D half-filled paramagnetic Hubbard model.The Luttinger critical exponents

The electronic system of the 1D Hubbard model is not stable due to Peierls instability; the correlations are strong even for the weak Coulomb interaction. The resulting strongly correlated state without Landau quisi--particle excitations is known as the Luttinger liquid. Critical exponents of a power--law dependence of correlation functions at low energies differ substantially for the Luttinger and Fermi liquids. In this paper we evaluate two critical exponents that define non--trivial behavior of the density of electronic states at low frequences and the momentum distribution of the occupation number nearby $k_F$.

cond-mat.str-el↗