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Materials Data on La3Ni2O7 by Materials Project

La3Ni2O7 is Orthorhombic Perovskite-like structured and crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are two inequivalent La3+ sites. In the first La3+ site, La3+ is bonded in a 4-coordinate geometry to eight O2- atoms. There are a spread of La–O bond distances ranging from 2.37–2.78 Å. In the second La3+ site, La3+ is bonded in a 11-coordinate geometry to eleven O2- atoms. There are a spread of La–O bond distances ranging from 2.38–3.00 Å. Ni+2.50+ is bonded to six O2- atoms to form corner-sharing NiO6 octahedra. The corner-sharing octahedra tilt angles range from 14–23°. There are a spread of Ni–O bond distances ranging from 1.97–2.21 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to four La3+ and two equivalent Ni+2.50+ atoms to form distorted OLa4Ni2 octahedra that share corners with two equivalent OLa4Ni2 octahedra, corners with four equivalent OLa4Ni square pyramids, an edgeedge with one OLa4Ni2 octahedra, faces with two equivalent OLa4Ni2 octahedra, and faces with two equivalent OLa4Ni square pyramids. The corner-sharing octahedral tilt angles are 65°. In the second O2- site, O2- is bonded in a 4-coordinate geometry to four La3+ and two equivalent Ni+2.50+ atoms. In the third O2- site, O2- is bonded to four equivalent La3+ and one Ni+2.50+ atom to form distorted OLa4Ni square pyramids that share corners with four equivalent OLa4Ni2 octahedra, corners with four equivalent OLa4Ni square pyramids, edges with four equivalent OLa4Ni square pyramids, and faces with two equivalent OLa4Ni2 octahedra. The corner-sharing octahedra tilt angles range from 38–55°. In the fourth O2- site, O2- is bonded in a 5-coordinate geometry to three equivalent La3+ and two equivalent Ni+2.50+ atoms.

36 MATERIALS SCIENCE↗

Superconductivity in Ruddlesden–Popper nickelates: a review of recent progress, focusing on thin films

The discovery of superconductivity with Tc ∼ 80 K in the nickelate Ruddlesden-Popper bilayer La3Ni2O7 at high pressure has opened a new platform for unconventional superconductivity, followed by the subsequent observation of superconductivity in trilayer La4Ni3O10, also at high pressure. Remarkably, ambient-pressure superconductivity was also observed recently in La3Ni2O7 ultra-thin films when grown on substrates that provide compressive strain. This discovery significantly extends the type of experimental techniques that can be used in nickelates, previously limited due to the high-pressure constraint. Discussing the similarities and differences among these nickel oxides will provide new insights into understanding the mechanism of high-Tc superconductivity in correlated electron systems. In this paper, we review the experimental and theoretical progress on Ruddlesden–Popper nickelates, with emphasis on thin films, and discuss future perspectives and research directions.

Zhang, Yang [ORNL] (ORCID:0000000336235883)↗

Spin Stripes and Superconductivity in Bilayer Nickelates

The bilayer nickelate La3Ni2O7 has recently emerged as a high-temperature superconductor with unusual spin stripe order in its ambient pressure phase. We propose a microscopic Hamiltonian that faithfully reflects the crystalline symmetry of this system, with the primary aim of addressing its unconventional magnetism at ambient pressure. Using state-of-the-art density matrix renormalization group calculations, we show that (π/2,π/2) spin stripe order arises in our model at sizable Hund's coupling JH from a hidden quasi-one-dimensionality and persists over a range of electron concentrations. In the more symmetric high-pressure regime, our model exhibits enhanced interlayer pairing tendencies when the interlayer antiferromagnetic coupling J⊥ becomes sufficiently large. Our results provide a microscopic origin of the diagonal spin stripes and identify Hund's coupling JH and interlayer coupling J⊥ as key ingredients governing magnetic order and pairing tendencies in La3Ni2O7.

Wang, Hao-Xin [The Chinese University of Hong Kong↗

The Quest for High-Temperature Superconductivity in Nickelates under Ambient Pressure

Recently, superconductivity with Tc ≈ 80 K was discovered in La3Ni2O7 under extreme hydrostatic pressure (>14 GPa). For practical applications, we needed to stabilize this state at ambient pressure. It was proposed that this could be accomplished by substituting La with Ba. To put this hypothesis to the test, we used the state-of-the-art atomic-layer-by-layer molecular beam epitaxy (ALL-MBE) technique to synthesize (La1−xBax)3Ni2O7 films, varying x and the distribution of La (lanthanum) and Ba (barium). Regrettably, none of the compositions we explored could be stabilized epitaxially; the targeted compounds decomposed immediately into a mixture of other phases. So, this path to high-temperature superconductivity in nickelates at ambient pressure does not seem promising.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗