REMARK ON THE EXISTENCE OF LONG-RANGE ORDER IN QUASI-TWO-DIMENSIONAL HUBBARD MODEL

1996 ◽  
Vol 10 (08) ◽  
pp. 341-346 ◽  
Author(s):  
A. BELKASRI ◽  
J.L. RICHARD
Keyword(s):  
Thin Film ◽  
High Temperature ◽  
Theoretical Analysis ◽  
Hubbard Model ◽  
Long Range ◽  
High Temperature Superconductivity ◽  
Type Model ◽  
Long Range Order ◽  
Two Dimensional ◽  
2D System

Recently in many works on the mechanism of high temperature superconductivity (see for example Refs. 1–6), quasi-averages like <ck↑c−k↓> were considered even in the case of a dimension less or equal two. But it is well known from the old work of Hohenberg7 that these quasi-averages are zero at T≠0 in case of 1 and 2 dimensions. In this communication we generalize the Hohenberg’s result to any kind of Hubbard type model on lattice and prove that in the case of quasi-two-dimension, the theorem of Hohenberg is not in contradiction with having <ck↑c−k↓>≠0 (at T≠0). In practice this makes sense to compare the data for a thin film (which can be considered as quasi-2D system) to the theoretical analysis based on quasi-two-dimensional models, but not for strictly two-dimensional case.

Phase diagram of cuprate high-temperature superconductors based on the optimization Monte Carlo method

2020 ◽  
Vol 34 (19n20) ◽  
pp. 2040046
Author(s):  
T. Yanagisawa ◽  
M. Miyazaki ◽  
K. Yamaji
Keyword(s):  
Phase Diagram ◽  
Monte Carlo ◽  
Wave Function ◽  
High Temperature ◽  
Hubbard Model ◽  
Ground State ◽  
State Energy ◽  
High Temperature Superconductivity ◽  
Two Dimensional ◽  
Text Model

It is important to understand the phase diagram of electronic states in the CuO2 plane to clarify the mechanism of high-temperature superconductivity. We investigate the ground state of electronic models with strong correlation by employing the optimization variational Monte Carlo method. We consider the two-dimensional Hubbard model as well as the three-band [Formula: see text]–[Formula: see text] model. We use the improved wave function that takes account of inter-site electron correlation to go beyond the Gutzwiller wave function. The ground state energy is lowered considerably, which now gives the best estimate of the ground state energy for the two-dimensional Hubbard model. The many-body effect plays an important role as an origin of spin correlation and superconductivity in correlated electron systems. We investigate the competition between the antiferromagnetic state and superconducting state by varying the Coulomb repulsion [Formula: see text], the band parameter [Formula: see text] and the electron density [Formula: see text] for the Hubbard model. We show phase diagrams that include superconducting and antiferromagnetic phases. We expect that high-temperature superconductivity occurs near the boundary between antiferromagnetic phase and superconducting one. Since the three-band [Formula: see text]–[Formula: see text] model contains many-band parameters, high-temperature superconductivity may be more likely to occur in the [Formula: see text]–[Formula: see text] model than in single-band models.

High-Temperature Superconductivity in Graphite-Sulfur Composites: Theoretical Analysis

2001 ◽  
Vol 689 ◽  
Author(s):  
D. S. Galvão ◽  
B. Laks ◽  
R. R. da Silva ◽  
J. H. S. Torres ◽  
Y. Kopelevich
Keyword(s):  
Electronic Structure ◽  
High Temperature ◽  
Theoretical Analysis ◽  
Density Of States ◽  
High Temperature Superconductivity ◽  
Tight Binding ◽  
Two Dimensional ◽  
Negative Factor ◽  
Structure Changes ◽  
Geometric Curvature

ABSTRACTRecently superconductivity in graphite-sulfur composites was experimentally observed. In this work we have analyzed the electronic structure changes associated with the presence of sulfur atoms in one and two dimensional graphite layers. We have considered ordered and disordered sulfur atoms distributions in many configurations. The density of states (DOS) of these structures were obtained using the negative factor counting (NFC) technique coupled to a tight-binding hamiltonian (Hückel type). Our results indicate that the incorporation of sulfur atoms at edge graphite layers (changing their global geometric curvature and increasing the DOS at the Fermi level) might be in the origin of the graphite superconductivity.

scholarly journals Recovery of long-range order in two-dimensional charge density waves at high temperatures

2021 ◽  
Vol 27 (S1) ◽  
pp. 952-954
Author(s):  
Suk Hyun Sung ◽  
Yin Min Goh ◽  
Noah Schnitzer ◽  
Ismail El Baggari ◽  
Kai Sun ◽  
...  
Keyword(s):  
Charge Density ◽  
Long Range ◽  
High Temperatures ◽  
Charge Density Waves ◽  
Range Order ◽  
Long Range Order ◽  
Two Dimensional ◽  
Density Waves

Controlling the Reactivity of C60: A Theoretical Analysis of the Electronic States Modulated by Substitutional Chemistry

1994 ◽  
Vol 359 ◽  
Author(s):  
S.-H. Wang ◽  
M. Kashani ◽  
S. Jansen
Keyword(s):  
High Temperature ◽  
Theoretical Analysis ◽  
High Temperature Superconductivity ◽  
Electronic States ◽  
Experimental Investigations ◽  
Cluster Stability ◽  
Simple Substitution ◽  
Doped Materials ◽  
Multiple Species

ABSTRACTThe availability of large amounts of Buckminsterfullerene has allowed a plethora of experimental investigations on fullerenes. The chemical and physical studies have focussed on synthesis, isomerism, magnetism, spectroscopy and high temperature superconductivity in doped materials. The chemical reactivities of fullerenes have been defined and most of the studies are dominated by C60 isomers. Some of the observed activities of fullerenes parlled those of alkeies. In our previous studies, the reactivity of the 6-6' bond with respect to eco- addition was described. Current studies have exploited the olefinic nature of the 6-6' bond and analyzed the effect of the addition on cluster stability and frontier character. In this work, we describe the mechanisms of simple substitution and analyze stability and orbital effects for the addition chemistry of C60 with multiple species. Evolving changes in orbital frontier character are analyzed with respect to site directed chemistry exhibited by C60.

scholarly journals Striped phases in the two-dimensional Hubbard model with long-range Coulomb interaction

1998 ◽  
Vol 58 (20) ◽  
pp. 13506-13509 ◽  
Author(s):  
G. Seibold ◽  
C. Castellani ◽  
C. Di Castro ◽  
M. Grilli
Keyword(s):  
Hubbard Model ◽  
Long Range ◽  
Coulomb Interaction ◽  
Two Dimensional ◽  
Striped Phases
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