Proposed ordering of textured spin singlets in a bulk infinite layer nickelate

Abstract

The infinite-layer structure nickelate Ba${}_2$NiO${}_2$(AgSe)${}_2$ (BNOAS) with $d^8$ Ni ions and a peculiar susceptibility $\chi (T)$ is studied with correlated density functional methods. The overriding feature of the calculations is violation of Hund's rule coupled with complete but unconventional spin-orbital polarization, leading to an unexpected low spin ${}^1{B}_1$, "off-diagonal singlet" (ODS) textured by an internal orbital structure of compensating $d_{x^2-y^2}^{\uparrow }$ and $d_{z^2}^{\downarrow }$ spins. This unconventional configuration has lower energy than conventional high-spin or low-spin alternatives. An electronic transition is obtained at a critical Ni-O separation $d_c^{Ni-O}=$2.03 Å, above which Ni becomes magnetic in square planar NiO${}_2$ compounds. We propose scenarios for the signature of magnetic reconstruction in $\chi (T)$ at $T_m$=130 K without any Curie-Weiss background (no moment) that invoke ordering of Ni $d^8$ moieties that are largely this generalized Kondo singlet. The underlying physics of this system is modeled by a Kondo sieve model (2D Kondo necklace) of a "Kondo" $d_{z^2}$ spin on each site, coupled to a $d_{x^2-y^2}$ spin that is itself strongly coupled to neighboring like-spins within the layer. The observed magnetic order places BNOAS below the quantum critical point of the Kondo sieve model, providing a realization of the previously unreported long-range ordered near-singlet weak antiferromagnetic phase. We propose electron doping experiments that would drive the system toward a $d^{9-\delta }$ configuration and possible superconductivity with similarity to the recently reported Ba${}_2$CuO${}_{3.2}$ that superconducts at 73 K.

12 pages (minor corrections)

References in corpus (4)

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• Self-doped Mott insulator for parent compounds of nickelate superconductors
• Anisotropy and Magnetism in the LSDA+U Method
• Role of $4f$ states in infinite-layer NdNiO${}_2$

Cited by in corpus (10)

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• Superconductivity in nickel based 112 systems
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• The dawn of the nickel age of superconductivity
• Low Valence Nickelates: Launching the Nickel Age of Superconductivity
• Screening in a two-band model for superconducting infinite-layer nickelate
• Two-band Conduction and Nesting Instabilities in Superconducting Ba${}_2$CuO${}_{3+\delta }$: a First Principles Study
• Field-induced Bose-Einstein condensation and supersolid in the two-dimensional Kondo necklace
• Magnetism of competing high-spin/low-spin states in Ba${}_2$NiO${}_2$(AgSe)${}_2$ and related two-orbital two-electron systems
• A $d^8$ anti-Hund's Singlet Insulator in an Infinite-layer Nickelate