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High-temperature materials.

Strongly Correlated Electrons and High Temperature Superconductivity

Takashi Yanagisawa

Published Jan 1, 2024• 1 citation
Publisher

Abstract

It is very important to clarify the mechanism of high-temperature superconductivity in strongly correlated electron systems. The mechanism of superconductivity in high temperature cuprate superconductors has been studied extensively since their discovery. We investigate the properties of correlated electron systems and mechanism of superconductivity by using the optimization quantum variational Monte Carlo method. The many-body wave function is constructed by multiplying by correlation operators of exponential type. We show that d-wave superconducting phase exists in the strongly correlated region where the on-site repulsive interaction is as large as the bandwidth or more than the bandwidth. The d-wave pairing correlation function is shown as a function of lattice sites, showing that the long-range order indeed exists.

DOI
10.35534/htm.2024.10004

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Abstract We investigate the ground state of the two-dimensional three-band d-p model for for high-temperature superconductors on the basis of a variational Monte Carlo method. We employ an optimization variational Monte Carlo method that we have developed recently. The many-body wave function is improved beyond the Gutzwiller ansatz by adopting the wave function in the form ψ = exp(−S)ψG where ψG represents the Gutzwiller function and S is a kinetic operator. The strong magnetic correlation and also superconductivity (SC) are induced by the on-site Coulomb repulsive interaction. It is important to clarify the phase diagram that includes superconductive phase and antiferromagnetic phase. We show the phase diagram to show the antiferromagnetic region in the parameter space. High-temperature superconductivity may occur in the strongly correlated region near the antiferromagnetic boundary.
Using the variational Monte Carlo method, we find that a relatively weak long-range electron-phonon interaction induces a ddd-wave superconducting state in doped Mott-Hubbard insulators and/or strongly correlated metals with a condensation energy significantly larger than can be obtained with Coulomb repulsion only. Moreover, the superconductivity is shown to exist for infinite on-site Coulomb repulsion without the need for additional mechanisms such as spin fluctuations to mediate ddd-wave superconductivity. We argue that our superconducting state is robust with respect to a more intricate choice of the trial-wave function and that a possible origin of high-temperature superconductivity lies in a proper combination of strong electron-electron correlations with poorly screened Fr\"ohlich electron-phonon interaction.