Electronic Band Structure and Madelung Potential Study of the Nickelates La(2)NiO(4), La(3)Ni(2)O(7), and La(4)Ni(3)O(10)

s^{±}-Wave Pairing and the Destructive Role of Apical-Oxygen Deficiencies in La_{3}Ni_{2}O_{7} under Pressure

Recently, the bilayer perovskite nickelate La_{3}Ni_{2}O_{7} has been reported to show evidence of high-temperature superconductivity (SC) under a moderate pressure of about 14 GPa. To investigate the superconducting mechanism, pairing symmetry, and the role of apical-oxygen deficiencies in this material, we perform a random-phase approximation based study on a bilayer model consisting of the d_{x^{2}-y^{2}} and d_{3z^{2}-r^{2}} orbitals of Ni atoms in both the pristine crystal and the crystal with apical-oxygen deficiencies. Our analysis reveals an s^{±}-wave pairing symmetry driven by spin fluctuations. The crucial role of pressure lies in that it induces the emergence of the γ pocket, which is involved in the strongest Fermi-surface nesting. We further found the emergence of local moments in the vicinity of apical-oxygen deficiencies, which significantly suppresses the T_{c}. Therefore, it is possible to significantly enhance the T_{c} by eliminating oxygen deficiencies during the synthesis of the samples.

Correlated Electronic Structure of La_{3}Ni_{2}O_{7} under Pressure

Recently, superconductivity with a T_{c} up to 78 K has been reported in bulk samples of the bilayer nickelate La_{3}Ni_{2}O_{7} at pressures above 14 GPa. Important theoretical tasks are the formulation of relevant low-energy models and the clarification of the normal state properties. Here, we study the correlated electronic structure of the high-pressure phase in a four-orbital low-energy subspace using different many-body approaches: GW, dynamical mean field theory (DMFT), extended DMFT (EDMFT) and GW+EDMFT, with realistic frequency-dependent interaction parameters. The nonlocal correlation and screening effects captured by GW+EDMFT result in an instability toward the formation of charge stripes, with the 3d_{z^{2}} as the main active orbital. We also comment on the potential relevance of the rare-earth self-doping pocket, since hole doping suppresses the ordering tendency.

Intertwined density waves in a metallic nickelate

Nickelates are a rich class of materials, ranging from insulating magnets to superconductors. But for stoichiometric materials, insulating behavior is the norm, as for most late transition metal oxides. Notable exceptions are the 3D perovskite LaNiO₃, an unconventional paramagnetic metal, and the layered Ruddlesden-Popper phases R₄Ni₃O₁₀, (R = La, Pr, Nd). The latter are particularly intriguing because they exhibit an unusual metal-to-metal transition. Here, we demonstrate that this transition results from an incommensurate density wave with both charge and magnetic character that lies closer in its behavior to the metallic density wave seen in chromium metal than the insulating stripes typically found in single-layer nickelates like La_2-xSr_xNiO₄. We identify these intertwined density waves as being Fermi surface-driven, revealing a novel ordering mechanism in this nickelate that reflects a coupling among charge, spin, and lattice degrees of freedom that differs not only from the single-layer materials, but from the 3D perovskites as well.

Layered Ruddlesden-Popper structure nickelates R₄Ni₃O₁₀ (R = La,Pr) show an unusual metal-to-metal transition, but its origin has remained elusive for more than two decades. Here, the authors show that this transition results from intertwined density waves that arise from a coupling between charge and spin degrees of freedom

Fermiology and electron dynamics of trilayer nickelate La4Ni3O10

Layered nickelates have the potential for exotic physics similar to high T_C superconducting cuprates as they have similar crystal structures and these transition metals are neighbors in the periodic table. Here we present an angle-resolved photoemission spectroscopy (ARPES) study of the trilayer nickelate La₄Ni₃O₁₀ revealing its electronic structure and correlations, finding strong resemblances to the cuprates as well as a few key differences. We find a large hole Fermi surface that closely resembles the Fermi surface of optimally hole-doped cuprates, including its \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$d_{x^2-y^2}$$\end{document}dx2-y2 orbital character, hole filling level, and strength of electronic correlations. However, in contrast to cuprates, La₄Ni₃O₁₀ has no pseudogap in the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$d_{x^2-y^2}$$\end{document}dx2-y2 band, while it has an extra band of principally \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$d_{3z^2-r^2}$$\end{document}d3z2-r2 orbital character, which presents a low temperature energy gap. These aspects drive the nickelate physics, with the differences from the cuprate electronic structure potentially shedding light on the origin of superconductivity in the cuprates.

Exploration of the electronic structure of nickelates with similar crystal structure to cuprates may shed a light on the origin of high T_c superconductivity. Here, Li et al. report strong resemblances and key differences of the electronic structure of trilayer nickelate La₄Ni₃O₁₀ compared to the cuprate superconductors.