Daily Overview: Today’s highlights focus on the in-depth understanding of the electronic structure of hybrid Ruddlesden-Popper nickelates. Using first-principles calculations, the researchers systematically revealed the crystal and electronic structural responses of La₇Ni₅O₁₇ under hydrostatic pressure and biaxial compressive strain, identifying a dynamically stable low-symmetry C2/c structure. It was found that both pressure and strain suppress octahedral tilting, leading to tetragonalization of the structure. The key difference lies in the Fermi level position of the d_z² bonding band in the trilayer block: under hydrostatic pressure, this band crosses the Fermi level at 30 GPa, whereas compressive strain consistently keeps it below the Fermi level. This strain-induced change in electronic structure is highly consistent with the behavior observed in conventional bilayer nickelates, providing crucial insights into the differentiated regulation of superconductivity by pressure and strain in this material system. arXiv submission processing window: 2026-03-18 00:00 to 2026-03-18 00:00 UTC.

1. Pressure and strain tuning of the alternating bilayer-trilayer Ruddlesden-Popper nickelate: crystal and electronic structure

Summary: Through first-principles calculations, this work investigates the crystal and electronic structures of the mixed bilayer-trilayer Ruddlesden-Popper nickelate La₇Ni₅O₁₇ under hydrostatic pressure and biaxial compressive strain. By analyzing the irreducible representations of dynamically unstable phonon modes in the high-symmetry P4/mmm structure, the authors identify a dynamically stable low-symmetry C2/c structure characterized by octahedral tilting. Both applied pressure and compressive strain suppress the octahedral tilting, leading to structural tetragonalization, a behavior akin to conventional Ruddlesden-Popper phases. In terms of electronic structure, the overall features under hydrostatic pressure and strain are similar, but a key difference lies in the position of the d_z² bonding band within the trilayer block: at 30 GPa pressure, this band crosses the Fermi level, whereas any magnitude of compressive strain keeps it below the Fermi level. This strain-induced electronic structure variation aligns with observations in conventional bilayer nickelates, offering critical insights into the distinct effects of pressure and strain on superconductivity in this class of materials.