Stability of the coexistent superconducting-nematic phase under the presence of intersite interactions

We analyze the effect of intersite-interaction terms on the stability of the coexisting superconucting-nematic phase (SC+N) within the extended Hubbard and $t$-$J$-$U$ models on the square lattice. In order to take into account the correlation effects with a proper precision, we use the approach based on the \textit{diagrammatic expansion of the Gutzwiller wave function} (DE-GWF), which goes beyond the renormalized mean field theory (RMFT) in a systematic manner. As a starting point of our analysis we discuss the stability region of the SC+N phase on the intrasite Coulomb repulsion-hole doping plane for the case of the Hubbard model. Next, we show that the exchange interaction term enhances superconductivity while suppresses the nematicity, whereas the intersite Coulomb repulsion term acts in the opposite manner. The competing character of the SC and N phases interplay is clearly visible throughout the analysis. A universal conclusion is that the nematic phase does not survive within the $t$-$J$-$U$ model with the value of $J$ integral typical for the high-T$_C$ cuprates ($J\approx 0.1$eV). For the sake of completeness, the effect of the correlated hopping term is also analyzed. Thus the present discussion contains all relevant two-site interaction terms which appear in the parametrized one-band model within the second quantization scheme. At the end, the influence of the higher-order terms of the diagrammatic expansion on the rotational symmetry breaking is also shown by comparing the DE-GWF results with those corresponding to the RMFT

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

The Hund's-rule-exchange induced and coexisting spin-triplet paired and magnetic states are considered within the doubly degenerate Hubbard model with interband hybridization. The Hartree-Fock approximation combined with the Bardeen-Cooper-Schrieffer (BCS) approach is analyzed for the case of square lattice. The calculated phase diagram contains regions of stability of the spin-triplet superconducting phase coexisting with either ferromagnetism or antiferromagnetism, as well as a pure superconducting phase. The influence of the inter-site hybridization on the stability of the considered phases, as well as the temperature dependence of both the magnetic moment and the superconducting gaps, are also discussed. Our approach supplements the well known phase diagrams containing only magnetic phases with the paired triplet states treated on the same footing. We also discuss briefly how to include the spin fluctuations within this model with real space pairing

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

We demonstrate the stability of a spin-triplet paired s-wave (with an admixture of extended s-wave) 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

Fulde-Ferrell state induced purely by the orbital effect in a superconducting nanowire

We demonstrate that the Fulde-Ferrell (FF) phase can be induced uniquely by the orbital effect in a cylindrical metallic nanowire. In the external magnetic field the two-fold degeneracy with respect to the orbital quantum number $m$ is lifted what leads to a Fermi wave vector mismatch between the subbands with opposite orbital momenta in the paired state. This mismatch can be compensated by the nonzero total momentum of the Cooper pairs created by electrons from split subbands what results in the formation of the FF phase. With increasing magnetic field a series of FF stability regions appear in between which the standard BCS superconducting phase is stable.Comment: 8 pages, 6 figure

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

The Gutzwiller wave function solution of the $t$-$J$-$U$ model is considered for the bilayer high-T$_C$ superconductor by using the so-called diagrammatic expansion method. The focus is on the influence of the interlayer effects on the superconducting state. The chosen pairing symmetry is a mixture of $d_{x^2-y^2}$ symmetry within the layers and the so-called $s^{\pm}$ symmetry for the interlayer contribution. The analyzed interlayer terms reflect the interlayer electron hopping, the interlayer exchange coupling, and the interlayer pair hopping. The obtained results are compared with selected experimental data corresponding to the copper-based compound Bi-2212 with two Cu-O planes in the unit cell. For the sake of comparison, selected results for the case of the bilayer Hubbard model are also provided. This paper complements our recent results obtained for the single-plane high temperature cuprates [cf. J. Spa{\l}ek, M. Zegrodnik, and J. Kaczmarczyk, Phys. Rev. B {\bf 95}, 024506 (2017)

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

We suggest that an inhomogeneous (non-zero momentum) paired phase can appear in the absence of an external magnetic field in the system with a predominant interband pairing and with separate Fermi-surface sheets. The Fermi wave vector mismatch which appears in such situation can be compensated by nonzero center-of-mass momentum of the Cooper pairs, what can lead to a spontaneous appearance of the Fulde-Ferrell type of superconducting state. The idea is examined using a tight-binding model which emulates the hole-like and the electron-like bands of iron based superconductor. The state can appear for the case of both spin-singlet and -triplet pairing channels

Autoimmunologiczne zapalenie części nerwowej i szypuły przysadki obejmujące również podwzgórze z towarzyszącym ogniskiem naciekowym w pniu mózgu : opis przypadku

Background: Autoimmune (lymphocytic) hypophysitis is a rare disease. It was originally labeled lymphocytic adenohypophysitis (LAH) and was first described in 1962. However, when it was later realized that the autoimmune infiltrate could exclusively involve the infundibular stem and the posterior lobe, the term lymphocytic infundibulo-neurohypophysitis (LINH) was created. Review of the literature identified 39 patients with LINH, 245 with LAH, and 95 with LPH (lymphocytic pan-hypophysitis) to date. Case Report: The authors present the case of a 19-year-old woman with acute bacterial infection previous to symptoms of hypopituitarism. CT and MR imaging showed tumor-like areas of intensive post-contrast enhancement without edema in the suprasellar region and in the brain stem. Based on the diagnostic investigations, LINH was diagnosed. Germinoma, sarcoidosis, tuberculosis, and bacterial hypophysitis were excluded in the diagnostic differentiation. Regression of clinical and radiological symptoms was observed after corticotherapy. Conclusions: Lymphocytic infundibulo-neurohypophysitis is a rare disease that should be considered in the differential diagnosis of any suprasellar and/or intrasellar mass