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Register a new userElectronic and Magnetic Structure of Infinite-layer $textrm{NdNiO}_2$: Trace of Antiferromagnetic Metal
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The recent discovery of Sr-doped infinite-layer nickelate $textrm{NdNiO}_2$ [D. Li et al. Nature 572, 624 (2019)] offers an exciting platform for investigating unconventional superconductivity in nickelatebased compounds. In this work, we present a first-principles calculations for the electronic and magnetic properties of undoped parent $textrm{NdNiO}_2$. Intriguingly, we found that: 1) the paramagnetic phase has complex Fermi pockets with 3D characters near the Fermi level; 2) by including electronelectron interactions, 3d-electrons of Ni tend to form $(pi, pi, pi)$ antiferromagnetic ordering at low temperatures; 3) with moderate interaction strength, 5d-electrons of Nd contribute small Fermi pockets that could weaken the magnetic order akin to the self-doping effect. Our results provide a plausible interpretation for the experimentally observed resistivity minimum and Hall coefficient drop. Moreover, we elucidate that antiferromagnetic ordering in $textrm{NdNiO}_2$ is relatively weak, arising from the small exchange coupling between 3d-electrons of Niand also hybridization with 5d-electrons of Nd.
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The demonstration of superconductivity in nickelate analogues of high $T_c$ cuprates provides new perspectives on the physics of correlated electron materials. The degree to which the nickelate electronic structure is similar to that of cuprates is an important open question. This paper presents results of a comparative study of the many-body electronic structure and theoretical phase diagram of the isostructural materials CaCuO$_2$ and NdNiO$_2$. Important differences include the proximity of the oxygen $2p$ bands to the Fermi level, the bandwidth of the transition metal-derived $3d$ bands, and the presence, in NdNiO$_2$, of both Nd-derived $5d$ states crossing the Fermi level and a van Hove singularity that crosses the Fermi level as the out of plane momentum is varied. The low energy physics of NdNiO$_2$ is found to be that of a single Ni-derived correlated band, with additional accompanying weakly correlated bands of Nd-derived states that dope the Ni-derived band. The effective correlation strength of the Ni-derived $d$-band crossing the Fermi level in NdNiO$_2$ is found to be greater than that of the Cu-derived $d$-band in CaCuO$_2$, but the predicted magnetic transition temperature of NdNiO$_2$ is substantially lower than that of CaCuO$_2$ because of the smaller bandwidth.
Motivated by the recent discovery of superconductivity in the infinite-layer (Sr,Nd)NiO$_2$ films with Sr content $x simeq0.2$ [Li et al., Nature (London) textbf{572}, 624 (2019)], we examine the effects of electron correlations and Sr-doping on the electronic structure, Fermi surface topology, and magnetic correlations in (Nd,Sr)NiO$_2$ using a combination of dynamical mean-field theory of correlated electrons and band-structure methods. Our results reveal a remarkable orbital selective renormalization of the Ni $3d$ bands, with $m$*/$msim 3$ and 1.3 for the $d_{x^2-y^2}$ and $d_{3z^2-r^2}$ orbitals, respectively, that suggests orbital-dependent localization of the Ni $3d$ states. We find that upon hole doping (Nd,Sr)NiO$_2$ undergoes a Lifshitz transition of the Fermi surface which is accompanied by a change of magnetic correlations from the three-dimensional (3D) Neel $G$-type (111) to the quasi-2D $C$-type (110). We show that magnetic interactions in (Nd,Sr)NiO$_2$ demonstrate an unanticipated frustration, which suppresses magnetic order, implying the importance of in-plane spin fluctuations to explain its superconductivity. Our results suggest that frustration is maximal for Sr-doping $x simeq 0.1$--0.2, which is in agreement with an experimentally observed doping value Sr $x simeq 0.2$ of superconducting (Nd,Sr)NiO$_2$.
We present a theoretical study of the effect of electron-electron interactions and Sr doping on the electronic structure of infinite-layer (Nd,Sr)NiO$_2$ using the density functional+dynamical mean-field theory approach. In particular, we explore the impact of epitaxial compressive strain that experience (Nd,Sr)NiO$_2$ films on the electronic properties, magnetic correlations, and exchange couplings. Our results reveal the crucial importance of orbital-dependent correlation effects in the Ni $3d$ shell of Sr-doped NdNiO$_2$. Upon doping with Sr, it undergoes a Lifshitz transition which is accompanied by a reconstruction of magnetic correlations: For Sr $x<0.2$ (Nd,Sr)NiO$_2$ adopts the Neel $(111)$ antiferromagnetic (AFM) order, while for $x>0.2$ the $C$-type $(110)$ AFM sets in the unstrained (Nd,Sr)NiO$_2$, with a highly frustrated region at $x simeq 0.2$, all within DFT+DMFT at $T=290$ K. Our results for the Neel AFM at Sr $x=0$ suggest that AFM NdNiO$_2$ appears at the verge of a Mott-Hubbard transition, providing a plausible explanation for the experimentally observed weakly insulating behavior of NdNiO$_2$ for Sr $x<0.1$. We observe that the Lifshitz transition makes a change of the band structure character from electron- to hole-like with Sr $x$, in agreement with recent experiments. Our results for magnetic couplings demonstrate an unanticipated frustration of the Ni $3d$ magnetic moments, which suppresses magnetic order near Sr $x=0.2$. We find that the effect of frustration is maximal for Sr doping $x simeq 0.1-0.2$ that nearly corresponds to the experimentally observed doping value. We conclude that the in-plane strain adjusts a bandwidth of the Ni $x^2-y^2$ band, i.e., controls the effect of electron correlations in the Ni $x^2-y^2$ orbitals. The electronic properties of (Nd,Sr)NiO$_2$ reveal an anomalous sensitivity upon a change of the crystal structure parameters.
We report on the electronic structure of the perovskite oxide CaCrO3 using valence-band, core-level, and Cr 2p - 3d resonant photoemission spectroscopy (PES). Despite its antiferromagnetic order, a clear Fermi edge characteristic of a metal with dominant Cr 3d character is observed in the valence band spectrum. The Cr 3d single particle density of states are spread over 2 eV, with the photoemission spectral weight distributed in two peaks centered at ~ 1.2 eV and 0.2 eV below EF, suggestive of the coherent and incoherent states resulting from strong electron-electron correlations. Resonant PES across the Cr 2p - 3d threshold identifies a two-hole correlation satellite and yields an on-site Coulomb energy U ~4.8 eV. The metallic DOS at EF is also reflected through the presence of a well-screened feature at low binding energy side of the Cr 2p core-level spectrum. X-ray absorption spectroscopy (XAS) at Cr L3,2 and O K edges exhibit small temperature dependent changes that point towards a small change in Cr-O hybridization. The multiplet splitting in Cr 2p core level spectrum as well as the spectral shape of the Cr XAS can be reproduced using cluster model calculations which favour a negative value for charge transfer energy between the Cr 3d and O 2p states. The overall results indicate that CaCrO3 is a strongly hybridized antiferromagnetic metal, lying in the regime intermediate to Mott-Hubbard and charge-transfer systems.
Using first-principles calculations, we analyze the evolution of the electronic structure and magnetic properties of infinite-layer nickelates RNiO$_2$ (R= rare-earth) as R changes across the lanthanide series from La to Lu. By correlating these changes with in-plane and out-of-plane lattice parameter reductions, we conclude that the in-plane Ni-O distance is the relevant control parameter in infinite-layer nickelates. An antiferromagnetic ground state is obtained for all RNiO$_2$ (R=La-Lu). This antiferromagnetic state remains metallic across the lanthanide series and is defined by a multiorbital picture with low-energy relevance of a flat Ni-d$_{z^2}$ band pinned at the Fermi level, in contrast to cuprates. Other non-cuprate-like properties such as the involvement of R-$d$ bands at the Fermi level, a large charge transfer energy, and a suppressed superexchange are robust for all RNiO$_2$ materials.
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