Daily Overview: Today’s highlights focus on advancing the understanding of the electronic structure of hybrid Ruddlesden–Popper nickelates. A study systematically reveals the pressure-driven structural phase transition (from a tilted Amam phase to an untilted phase) in bilayer nickel oxide La₃Ni₂O₇ using high-pressure high-temperature Raman and infrared spectroscopy, along with the accompanying evolution of electronic properties: the transition increases the carrier density by nearly two orders of magnitude, marking a crossover from a bad metal to a good metal, and is closely correlated with the pressure range (approximately 6–7 GPa) where superconductivity emerges. However, high symmetry and metallicity alone are insufficient to induce superconductivity, suggesting that strong electronic correlation effects, such as density wave fluctuations, may play a crucial role, providing important experimental constraints for understanding the mechanism of nickel-based superconductivity. arXiv submission processing window: 2026-05-03 00:25 to 2026-05-03 00:25 UTC.
1. Metallic crossover through the tilt-free transition in La$_3$Ni$_2$O$_7$ at high pressure and temperature
- Relevance Score:
5.8687 - Authors: Bastien Michon, Yingpeng Yu, Beatrice D’Alò, Elena Stellino, Gergely Németh, Bosen Wang, Jianping Sun, Jinguang Cheng, Paolo Postorino, Ferenc Borondics, Francesco Capitani
- Affiliations: Université Paris-Saclay
- Link: http://arxiv.org/abs/2605.01651v1
- Paper page: Metallic crossover through the tilt-free transition in La₃Ni₂O₇ at high pressure and temperature
Summary: This study systematically investigates the structural phase transitions and electronic property evolution of the bilayer nickelate La₃Ni₂O₇ under pressure and temperature using high-pressure high-temperature Raman spectroscopy and synchrotron infrared reflectance spectroscopy. Raman measurements confirm a pressure-driven structural phase transition from the tilted Amam phase to the untilted Fmmm or I4/mmm phase, with the emergence of Fano line shapes indicating enhanced electron-phonon coupling. High-temperature data reveal an upper temperature limit of 544 K for this transition at ambient pressure, refining the temperature-pressure phase diagram. Infrared reflectivity measurements show that the phase transition is accompanied by an increase in carrier density by nearly two orders of magnitude, marking a crossover from a bad metal to a good metal. The experiments establish a unified picture where the structural phase transition is strongly coupled to electronic properties, with superconductivity emerging at approximately 6-7 GPa closely associated with the appearance of the untilted phase; however, high symmetry and metallicity alone are insufficient to induce superconductivity, suggesting that strong electronic correlation effects such as density wave fluctuations may also need to be considered.