Realization of a classical Ruddlesden Popper type bilayer nickelate in Sr$_3$Ni$_{2-x}$Al$_{x}$O$_{7-\delta}$ with unusual Ni$^{4+}$

Hasan Yilmaz; Kathrin Küster; Ulrich Starke; Oliver Clemens; Masahiko Isobe; Pascal Puphal

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arXiv · 2406.12453

Realization of a classical Ruddlesden Popper type bilayer nickelate in Sr$_3$Ni$_{2-x}$Al$_{x}$O$_{7-\delta}$ with unusual Ni$^{4+}$

Hasan Yilmaz·Kathrin Küster·Ulrich Starke·Oliver Clemens·Masahiko Isobe·Pascal Puphal

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Abstract

The discovery of 80 K superconductivity in bilayer La$_3$Ni$_2$O$_7$ at pressures greater than 14 GPa presents a unique opportunity to study a novel class of high-temperature superconductors. Therefore, other bilayer nickelate following the classical ($T^{4+}$) Ruddlesden-Popper (RP) series of Sr$_3$Ni$_2$O$_7$ would present an interesting new candidate. In this work, we study the stabilization of RP $n=2$ phase in Sr$_3$Ni$_{2-x}$Al$_{x}$O$_7$, via floating zone growth of crystals. With powder and single crystal XRD, we study the stability range of the RP-type phase. Our Thermogravimetric Analysis (TGA), X-ray photoelectron spectroscopy (XPS) and gas extraction studies reveal a remarkably high oxidation state of Ni$^{4+}$. The obtained black crystals are insulating in transport and show a magnetic transition around 12 K.

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Hasan Yilmaz, Kathrin Küster, Ulrich Starke, Oliver Clemens, Masahiko Isobe, Pascal Puphal. 2024-06-18. Realization of a classical Ruddlesden Popper type bilayer nickelate in Sr$_3$Ni$_{2-x}$Al$_{x}$O$_{7-\delta}$ with unusual Ni$^{4+}$. https://arxiv.org/abs/2406.12453

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