Michał Zegrodnik

Even-parity spin-triplet pairing by purely repulsive interactions for orbitally degenerate correlated fermions

We demonstrate the stability of a spin-triplet paired s-wave (with an admixture of extended swave) state for the case of purely repulsive interactions in a degenerate two-band Hubbard model. We further show that near half-filling the considered kind of superconductivity can coexist with antiferromagnetism. The calculations have been carried out with the use of the so-called statistically consistent Gutzwiller approximation for the case of a square lattice. The absence of a stable paired state when analyzed in the Hartree-Fock-BCS approximation allows us to claim that the electron correlations in conjunction with the Hund’s rule exchange play the crucial role in stabilizing the spin-triplet superconducting state. A sizable hybridization of the bands suppresses the paired state.We demonstrate the stability of the spin-triplet paired s-wave (with an admixture of extended s-wave) state for the limit of purely repulsive interactions in a degenerate two-band Hubbard model of correlated fermions. The repulsive interactions limit represents an essential extension of our previous analysis (2013 New J. Phys. 15 073050), regarded here as I. We also show that near the half-filling the considered type of superconductivity can coexist with antiferromagnetism. The calculations have been carried out with the use of the so-called statistically consistent Gutzwiller approximation (SGA) for the case of a square lattice. We suggest that the electron correlations in conjunction with the Hunds rule exchange play the crucial role in stabilizing the real-space spin-triplet superconducting state. A sizable hybridization of the bands suppresses the homogeneous paired state.

Coexistence of spin-triplet superconductivity with magnetism within a single mechanism for orbitally degenerate correlated electrons: statistically consistent Gutzwiller approximation

An orbitally degenerate two-band Hubbard model is analyzed with the inclusion of the Hunds rule-induced spin-triplet even-parity paired states and their coexistence with magnetic ordering. The so-called statistically consistent Gutzwiller approximation (SGA) has been applied to the case of a square lattice. The superconducting gaps, the magnetic moment and the free energy are analyzed as a function of the Hunds rule coupling strength and the band filling. Also, the influence of the intersite hybridization on the stability of paired phases is discussed. In order to examine the effect of correlations the results are compared with those calculated earlier within the Hartree-Fock (HF) approximation combined with the Bardeen-Cooper-Schrieffer (BCS) approach. Significant differences between the two methods used (HF+BCS versus SGA+real-space pairing) appear in the stability regions of the considered phases. Our results supplement the analysis of this canonical model used

Spin-triplet paired state induced by Hund's rule coupling and correlations: a fully statistically consistent Gutzwiller approach.

The intrasite and intersite spin-triplet pairing gaps induced by interband Hunds rule coupling and their correlations are analyzed in the doubly degenerate Hubbard Hamiltonian. To include the effect of correlations, the statistically consistent Gutzwiller approximation is used. In this approach the consistency means that the averages calculated from the self-consistent equations and those determined variationally coincide with each other. Emphasis is put on the solution for which the average particle number is conserved when carrying out the Gutzwiller projection. This method leads to a stable equal-spin paired state in the so-called repulsive interactions limit (U > 3J) in the regime of moderate correlations. The interband hybridization introduces an inequivalence of the bands which, above a critical magnitude, suppresses the paired state due to both the Fermi-wavevector mismatch for the Cooper pair and the interband hopping allowed by the Pauli principle.

Universal properties of high-temperature superconductors from real-space pairing : t − J − U model and its quantitative comparison with experiment

Selected universal experimental properties of high temperature superconducting (HTS) cuprates have been singled out in the last decade. One of the pivotal challenges in this field is the designation of a consistent interpretation framework within which we can describe quantitatively the universal features of those systems. Here we analyze in a detailed manner the principal experimental data and compare them quantitatively with the approach based on a single band of strongly correlated electrons supplemented with strong antiferromagnetic (super)exchange interaction (the so-called

Coexistence of spin-triplet superconductivity with magnetic ordering in an orbitally degenerate system: Hartree-Fock-BCS approximation revisited

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Quantum size effect on the paramagnetic critical field in free-standing superconducting nanofilms

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Universal properties of high-temperature superconductors from real-space pairing: Role of correlated hopping and intersite Coulomb interaction within the t−J−U model

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Spontaneous appearance of nonzero-momentum Cooper pairing: Possible application to the iron-pnictides

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Antiferromagnetism, charge density wave, and d-wave superconductivity in the extended t-J-U model: role of intersite Coulomb interaction and a critical overview of renormalized mean field theory

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Effect of interlayer processes on the superconducting state within the t-J-U model: Full Gutzwiller wave-function solution and relation to experiment

model). The model rationale is provided by estimating its macroscopic parameters on the basis of the 3-band approach for the Cu-O plane. We use our original full Gutzwiller-wave-function solution by going beyond the renormalized mean field theory (RMFT) in a systematic manner. Our approach reproduces very well the observed hole doping (