Abstract
The authors study the magnitude of the magnetic exchange coupling in theoretically-proposed cuprate-analog nickelates, and shows that the nickelates share a common thread with the cuprates in that they also have a significant exchange coupling as large as about 100 meV.
Highlights
The agreement in the order estimate of J among three independent methods shows that RbCa2NiO3 and A2NiO2Br2 (A = Ba0.5La0.5) are Mott insulators, with the effective model being the Heisenberg model, and the magnetic exchange coupling J is governed by the superexchange interaction [if the materials were, for example, weakly correlated, the three methods would not agree well
We have evaluated the size of J for d9 nickelates from first principles
While the cuprates having small d p belong to the charge-transfer type in the Zaanen-Sawatzky-Allen diagram [54], nickelates with larger d p belong to the Mott-Hubbard type
Summary
The discovery of superconductivity in doped nickel oxides Nd0.8Sr0.2NiO2 [1,2] has attracted intensive interest in both experiment [3,4,5,6,7,8,9,10,11,12,13] and theory [3,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52] because the nickelate might be an analog of the well-known high-Tc superconductor, cuprates. One of the reasons for the controversy in theory about the size of J [20,21,22,23,24,25,26,27,28,29] is ascribed to the ambiguity in calculating J (whether we calculate J at d9 filling or J including the self-doping effect) In any case, it is a nontrivial problem whether we can justify the mapping onto a simple spin model to understand the property of NdNiO2. An ab initio estimate of Hubbard U using the constrained random-phase approximation (cRPA) [58] shows that the correlation strength U/t (t denotes nearest-neighbor hopping) is comparable to that of cuprates [18] Once such nickelates are synthesized, the mother compounds will be a Mott insulator to the cuprates and the effective model becomes the Heisenberg model, which gets rid of the ambiguity in calculating J.
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