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arXiv · 2412.19617

Interplay of orbital-selective Mott criticality and flat-band physics in La$_3$Ni$_2$O$_6$

Frank Lechermann·Steffen Bötzel·Ilya M. Eremin
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Abstract

Superconductivity in nickelates apparently takes place in two different Ni oxidation regimes, namely either for infinite-layer-type compounds close to Ni$^{+}$, or for Ruddlesden-Popper materials close to Ni$^{2+}$. The reduced La$_3$Ni$_2$O$_6$ bilayer with a nominal Ni$^{1.5+}$ oxidation state may therefore serve as a normal-state mediator between the two known families of $3d^8$-like and $3d^9$-like superconducting nickelates. Using first-principles many-body theory, we explain its experimental 50\,meV charge gap as originating from a new type of correlated (quasi-)insulator. Flat-band electrons of Ni-$d_{z^2}$ character become localized from scattering with orbital-selective Mott-localized Ni-$d_{x^2-y^2}$ electrons, by trading in residual hopping energy for a gain in local exchange energy in a ferromagnetic Kondo-lattice scenario. Most importantly, the flat-band electrons offer another route to unconventional superconductivity in nickelates at ambient pressure.

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Frank Lechermann, Steffen Bötzel, Ilya M. Eremin. 2024-12-27. Interplay of orbital-selective Mott criticality and flat-band physics in La$_3$Ni$_2$O$_6$. https://doi.org/10.1103/3r7g-89r8

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