scholarly journals Superconductivity, Antiferromagnetism, and Kinetic Correlation in Strongly Correlated Electron Systems

2015 ◽  
Vol 2015 ◽  
pp. 1-5
Author(s):  
Takashi Yanagisawa
Keyword(s):  
High Temperature ◽  
Hubbard Model ◽  
High Temperature Superconductivity ◽  
Spin Fluctuation ◽  
Coulomb Repulsion ◽  
Strongly Correlated Electron ◽  
Correlated Electron Systems ◽  
Correlated Electron ◽  
Antiferromagnetic Correlation ◽  
The Stability

We investigate the ground state of two-dimensional Hubbard model on the basis of the variational Monte Carlo method. We use wave functions that include kinetic correlation and doublon-holon correlation beyond the Gutzwiller ansatz. It is still not clear whether the Hubbard model accounts for high-temperature superconductivity. The antiferromagnetic correlation plays a key role in the study of pairing mechanism because the superconductive phase exists usually close to the antiferromagnetic phase. We investigate the stability of the antiferromagnetic state when holes are doped as a function of the Coulomb repulsionU. We show that the antiferromagnetic correlation is suppressed asUis increased exceeding the bandwidth. High-temperature superconductivity is possible in this region with enhanced antiferromagnetic spin fluctuation and pairing interaction.

scholarly journals Crossover Induced Electron Pairing and Superconductivity by Kinetic Renormalization in Correlated Electron Systems

2018 ◽  
Vol 3 (3) ◽  
pp. 26 ◽  
Author(s):  
Takashi Yanagisawa ◽  
Mitake Miyazaki ◽  
Kunihiko Yamaji
Keyword(s):  
Wave Function ◽  
High Temperature ◽  
High Temperature Superconductivity ◽  
Electron System ◽  
Strongly Correlated ◽  
Electron Systems ◽  
Strongly Correlated Electron ◽  
Correlated Electron Systems ◽  
Correlated Electron ◽  
The Many

We investigate the ground state of strongly correlated electron systems based on an optimization variational Monte Carlo method to clarify the mechanism of high-temperature superconductivity. The wave function is optimized by introducing variational parameters in an exponential-type wave function beyond the Gutzwiller function. The many-body effect plays an important role as an origin of superconductivity in a correlated electron system. There is a crossover between weakly correlated region and strongly correlated region, where two regions are characterized by the strength of the on-site Coulomb interaction U. We insist that high-temperature superconductivity occurs in the strongly correlated region.

Strongly Correlated Electron Systems: Spin-Reflection Positivity and Some Rigorous Results

1998 ◽  
Vol 12 (07n08) ◽  
pp. 709-779 ◽  
Author(s):  
Shun-Qing Shen
Keyword(s):  
Hubbard Model ◽  
Long Range ◽  
Strongly Correlated Electron Systems ◽  
Strongly Correlated ◽  
Electron Systems ◽  
Strongly Correlated Electron ◽  
Rigorous Results ◽  
Correlated Electron Systems ◽  
Correlated Electron ◽  
Generalized Hubbard Model

Theory of spin-reflection positivity developed in recent years is reviewed. This theory makes use of symmetries in an electron system and theory of matrix to investigate the ground state properties. Existences of anti- and ferromagnetic long-range orders in itinerant electron systems, and of off-diagonal long-range order are two successful applications of the theory. In this article, the author attempt to summarize exact results proved by utilizing this theory and related topics. First a general theory and basic theorems are introduced. Second, based on the band structures of conduction electrons, existences of a singlet state with strongly antiferromagnetic correlation, a state with both anti- and ferromagnetic long-range orders, and a fully saturated ferromagnetic state are proved. The theory is applied to several of the main theoretical models for strongly correlated electron systems, such as the Heisenberg model, the Hubbard model, the Anderson model, the single- and multichannel Kondo model, and the generalized Hubbard model, and a series of rigorous results are found in these models. Third, it is proved that off-diagonal long-range order and charge-density wave exist in the ground states of the attractive Hubbard model and the generalized Hubbard model. A relation between pseudospin symmetry and the uniform density theorem is introduced. Fourth, the theory is applied successfully to explain experimental observations of oscillatory interlayer magnetic coupling in ultrathin magnetic films. Finally several unsolved problems are discussed. All results introduced in this article are mathematically exact.

scholarly journals Unusual symmetries of the order parameter in cuprates

2020 ◽  
Vol 2 (4) ◽  
pp. 207-212
Author(s):  
Tran Van Luong ◽  
Nguyen Thi Ngoc Nu
Keyword(s):  
High Temperature ◽  
Order Parameter ◽  
Cuprate Superconductors ◽  
High Temperature Superconductivity ◽  
Spin Fluctuation ◽  
High Temperature Superconductors ◽  
Coulomb Repulsion ◽  
Bcs Theory ◽  
S Wave ◽  
Wave Symmetry

The BCS superconducting theory, introduced by J. Bardeen, L. Cooper and R. Schriffer in 1957, succeeded in describing and satis-factorily explaining the nature of superconductivity for low-temperature superconductors. However, the BCS theory cannot explain the properties of high-temperature superconductors, discovered by J. G. Bednorz and K. A. Müller in 1986. Although scientists have found a lot of new superconductors and their transition temperatures are constantly increasing, most high-temperature superconductors are found by experiment and so far no theory can fully explain their properties. Many previous studies have suggested that the order parameter in high-temperature copper-based superconductors (cuprate superconductors - cuprates) is in the form of d-wave symmetry, but recent results show that the order parameter has an extended s-wave symmetry (extended s wave). Studying the symmetric forms of order parameters in cuprate can contribute to understanding the nature of high-temperature superconductivity. In this article, the authors present an overview of the development of high-temperature supercon-ductors over the past 30 years and explains unusual symmetries of the order parameter in copper-based superconductors. The com-petition of three coupling mechanisms of electrons in cuprates (the mechanism of coupling through coulomb repulsion, electron-phonon mechanism and spin-fluctuation mechanism) affects the unusual symmetry of the order parameter. The solution of the self-consistency equation in simple cases has been found and the ability to move the phase within the superconducting state has been shown.

scholarly journals RAMAN SCATTERING IN IRON-BASED SUPERCONDUCTORS

2012 ◽  
Vol 26 (28) ◽  
pp. 1230020 ◽  
Author(s):  
A. M. ZHANG ◽  
Q. M. ZHANG
Keyword(s):  
High Temperature ◽  
Raman Scattering ◽  
Cuprate Superconductors ◽  
High Temperature Superconductivity ◽  
Industrial Applications ◽  
Layered Compounds ◽  
Correlated Electron Systems ◽  
Correlated Electron ◽  
History Of ◽  
Iron Based

Iron-based superconducting layered compounds have the second highest transition temperature after cuprate superconductors. Their discovery is a milestone in the history of high-temperature superconductivity and will have profound implications for high-temperature superconducting mechanism as well as industrial applications. Raman scattering has been extensively applied to correlated electron systems including the new superconductors due to its unique ability to probe multiple primary excitations and their coupling. In this review, we will give a brief summary of the existing Raman experiments in the iron-based materials and their implications for pairing mechanism in particular. And we will also address some open issues from the experiments.

DYNAMICS OF HOLES IN THE Cu-OXIDE SUPERCONDUCTORS

1989 ◽  
Vol 03 (16) ◽  
pp. 1191-1195 ◽  
Author(s):  
J. INOUE ◽  
S. MAEKAWA
Keyword(s):  
Valence Bond ◽  
Oxide Superconductors ◽  
Strongly Correlated ◽  
Electron Systems ◽  
Strongly Correlated Electron ◽  
Correlated Electron Systems ◽  
Correlated Electron ◽  
Bond State ◽  
Recent Developments ◽  
The Stability

Recent developments of our work on the dynamics of holes in strongly correlated electron systems and on the stability of the resonating valence bond state are summarized.

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