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Metallic crossover through the tilt-free transition in La3Ni2O7 at high pressure and temperature

Bastien Michon1,*,†, Yingpeng Yu2,3, Beatrice D'Alò1, Elena Stellino4, Gergely Németh1, Bosen Wang2,3, Jianping Sun2,3, Jinguang Cheng2,3, Paolo Postorino5 et al.

Ferenc Borondics1 and Francesco Capitani1

  • *Contact author: bastien.michon@univ-tours.fr
  • †Present address: GREMAN - UMR7347 CNRS, Université de Tours, INSA Centre Val de Loire, Parc de Grandmont, 37200 Tours, France.
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Phys. Rev. B 114, L140102 – Published 1 September, 2026

DOI: https://doi.org/10.1103/832c-p7qj

Abstract

La3Ni2O7, a bilayer nickelate with Ruddlesden-Popper structure, undergoes a pressure-induced structural transition from a tilted Amam phase to an untilted Fmmm (or I4/mmm) phase near 10–15 GPa, concomitant with the emergence of high-Tc superconductivity (Tc∼80K). Despite intense interest, the phase boundaries and the impact of structural changes on the electronic properties remain unclear. Here, we combine high-pressure and high-temperature Raman and synchrotron-based infrared spectroscopies to map the structural and electronic evolutions. Raman measurements confirm the pressure-driven structural transition and reveal the emergence of Fano line shapes, indicating enhanced electron-phonon coupling. High-temperature data show analogous spectral signatures above 544 K, suggesting an upper temperature limit of the Amam phase within the T-P phase diagram of this system. Infrared reflectivity measurements evidence a concomitant enhanced metallicity, with a tremendous two-order-of-magnitude increase in carrier density, marking a crossover from a weakly to highly metallic state. These results establish a unified picture of the structural transition and its strong coupling to the electronic properties.

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Phys. Rev. B 114, L140102– Published 1 September, 2026
  • Received 26 May 2026
  • Accepted 14 August 2026
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