scholarly journals Correlated-Electron Systems and High-Temperature Superconductivity

2013 ◽  
Vol 04 (06) ◽  
pp. 33-64 ◽  
Author(s):  
Takashi Yanagisawa ◽  
Mitake Miyazaki ◽  
Kunihiko Yamaji
Keyword(s):  
High Temperature ◽  
High Temperature Superconductivity ◽  
Electron Systems ◽  
Correlated Electron Systems ◽  
Correlated Electron

scholarly journals Mechanism of High-Temperature Superconductivity in Correlated-Electron Systems

2019 ◽  
Vol 4 (2) ◽  
pp. 57 ◽  
Author(s):  
Takashi Yanagisawa
Keyword(s):  
High Temperature ◽  
High Temperature Superconductivity ◽  
High Temperature Superconductors ◽  
Energy Scale ◽  
Strongly Correlated ◽  
Electron Systems ◽  
Strong Electron ◽  
Correlated Electron Systems ◽  
Correlated Electron ◽  
Variational Monte Carlo Method

It is very important to elucidate the mechanism of superconductivity for achieving room temperature superconductivity. In the first half of this paper, we give a brief review on mechanisms of superconductivity in many-electron systems. We believe that high-temperature superconductivity may occur in a system with interaction of large-energy scale. Empirically, this is true for superconductors that have been found so far. In the second half of this paper, we discuss cuprate high-temperature superconductors. We argue that superconductivity of high temperature cuprates is induced by the strong on-site Coulomb interaction, that is, the origin of high-temperature superconductivity is the strong electron correlation. We show the results on the ground state of electronic models for high temperature cuprates on the basis of the optimization variational Monte Carlo method. A high-temperature superconducting phase will exist in the strongly correlated region.

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.

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.

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.

Strongly correlated superconductivity

2018 ◽  
Vol 32 (17) ◽  
pp. 1840023
Author(s):  
T. Yanagisawa ◽  
M. Miyazaki ◽  
K. Yamaji
Keyword(s):  
High Temperature Superconductivity ◽  
Strongly Correlated ◽  
Electron Systems ◽  
Many Body ◽  
Strongly Correlated Electron ◽  
Correlated Electron Systems ◽  
Correlated Electron ◽  
Repulsive Coulomb ◽  
Variational Monte Carlo Method ◽  
The Many

We investigate the electronic properties of the ground state of strongly correlated electron systems. We use an optimization variational Monte Carlo method for the two-dimensional Hubbard model and the three-band d-p model. The many-body wavefunction is improved and optimized by introducing variational parameters that control the correlation between electrons. The on-site repulsive Coulomb interaction U induces strong antiferromagnetic (AF) correlation. There is a crossover from weakly to strongly correlated regions as U increases. We show an idea that high-temperature superconductivity occurs as a result of this crossover in the strongly correlated region where U is greater than the bandwidth.

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