High temperature transitions in Ruddlesden-Popper nickelates La$_{n+1}$Ni$_{n}$O$_{3n+1}$

P. Reiss; A. Shevchenko; P. S. Lizama; J. Nuss; R. Dinnebier; P. A. van Aken; M. Hepting; M. Isobe; Y. E. Suyolcu; H. Takagi; B. Keimer; P. Puphal

arXiv · 2606.27040

High temperature transitions in Ruddlesden-Popper nickelates La$_{n+1}$Ni$_{n}$O$_{3n+1}$

P. Reiss·A. Shevchenko·P. S. Lizama·J. Nuss·R. Dinnebier·P. A. van Aken·M. Hepting·M. Isobe·Y. E. Suyolcu·H. Takagi·B. Keimer·P. Puphal

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Abstract

The discovery of superconductivity at $15\,\mathrm{K}$ in the infinite-layer nickelate $(\mathrm{Nd},\mathrm{Sr})\mathrm{NiO}_2$, followed by superconductivity at $80\,\mathrm{K}$ in the Ruddlesden--Popper phase $\mathrm{La}_3\mathrm{Ni}_2\mathrm{O}_7$, has ushered in a new era of nickelate research. Despite this progress, large discrepancies between reports exist. Here, we investigate the complete series of bulk-stable $\mathrm{La}_{n+1}\mathrm{Ni}_n\mathrm{O}_{3n+1}$ compounds using a comprehensive set of experimental techniques, including PXRD, single-crystal XRD, electron microscopy, heat capacity, differential scanning calorimetry, magnetic susceptibility, and transport measurements, over a broad temperature range from $2$ to $1000\,\mathrm{K}$. By studying high-quality single crystals, we identify a previously underappreciated high-temperature phase transition in Ruddlesden--Popper nickelates $\mathrm{La}_{n+1}\mathrm{Ni}_n\mathrm{O}_{3n+1}$ distinct from the one going to a tetragonal phase.

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P. Reiss, A. Shevchenko, P. S. Lizama, J. Nuss, R. Dinnebier, P. A. van Aken, M. Hepting, M. Isobe, Y. E. Suyolcu, H. Takagi, B. Keimer, P. Puphal. 2026-06-25. High temperature transitions in Ruddlesden-Popper nickelates La$_{n+1}$Ni$_{n}$O$_{3n+1}$. https://arxiv.org/abs/2606.27040

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