The double perovskite ${\rm La}_2{\rm NiTiO}_6$ is identified as a three-dimensional $S=1$ quantum magnet. By means of Density Functional Theory we demonstrate that this material is a high-spin $d$-electron system deep in the Heisenberg limit and establish that its paramagnetic Mott phase persists down to low temperatures ($T_{\rm N}$=25K) not because of frustration effects but rather for the extreme strong coupling physics. Our many-body calculations on an $ab$ $initio$-derived multi-orbital basis predict indeed a kinetic energy gain when entering the magnetically ordered phase. ${\rm La}_2{\rm NiTiO}_6$ emerges thus as a paradigmatic realization of a spin-triplet Mott insulator. Its peculiar properties may turn out to be instrumental in the ongoing chase after correlated topological states of matter.
The RNiO$_3$ perovskites are known to order antiferromagnetically below a material-dependent Néel temperature $T_\text{N}$. We report experimental evidence indicating the existence of a second magnetically-ordered phase in TlNiO$_3$ above $T_\text{N} = 104$ K, obtained using nuclear magnetic resonance and muon spin rotation spectroscopy. The new phase, which persists up to a temperature $T_\text{N}^* = 202$ K, is suppressed by the application of an external magnetic field of approximately 1 T. It is not yet known if such a phase also exists in other perovskite nickelates.
We report on tunneling measurements that reveal for the first time the evolution of the quasi-particle state density across the bandwidth controlled Mott metal to insulator transition in the rare earth perovskite nickelates. In this, a canonical class of transition metal oxides, we study in particular two materials close to the T=0 metal-insulator transition: NdNiO3 , an antiferromagnetic insulator, and LaNiO3, a correlated metal. We measure a sharp gap in NdNiO3, which has an insulating ground state, of ~ 30 meV. Remarkably, metallic LaNiO3 exhibits a pseudogap of the same order that presages…
The perovskite nickelates RNiO$_3$ (R: rare-earth) have been studied as potential multiferroic compounds. A certain degree of charge disproportionation in the Ni ions has been confirmed by high resolution synchrotron power diffraction: instead of the nominal Ni$^{3+}$ valence, they can have the mixed-valence state Ni$^{(3-δ)+}$ and Ni$^{(3+δ)+}$, though agreement has not been reached on the precise value of $δ$ (e.g. for NdNiO$_3$, $δ=0.0$ and $δ=0.29$ were reported). Also, the magnetic ground state is not yet clear: collinear and non-collinear Ni-O magnetic structures have been proposed to ex…
A full implementation of the $ab$ $initio$ density functional plus dynamical mean field theory (DFT+DMFT) formalism to perform total energy calculations and structural relaxations is proposed and implemented. The method is applied to the structural and metal-insulator transitions of the rare earth nickelate perovskites as a function of rare earth ion, pressure, and temperature. In contrast to previous DFT and DFT+$U$ theories, the present method accounts for the experimentally observed structure of $La$NiO$_3$ and the insulating nature of the other perovskites, and quantitatively reproduces th…
Rare-earth nickelates R$^{3+}$Ni$^{3+}$O$_3$ (R=Lu-Pr, Y) show a striking metal-insulator transition in their bulk phase whose temperature can be tuned by the rare-earth radius. These compounds are also the parent phases of the newly identified infinite layer RNiO2 superconductors. Although intensive theoretical works have been devoted to understand the origin of the metal-insulator transition in the bulk, there have only been a few studies on the role of hole and electron doping by rare-earth substitutions in RNiO$_3$ materials. Using first-principles calculations based on density functional …
From perovskite to infinite-layer nickelates: hole concentration from x-ray absorption
Max Planck Institute for Solid State Research（马克斯·普朗克固体研究所）；Universite de Strasbourg, CNRS, IPCMS UMR 7504（斯特拉斯堡大学）；Helmholtz-Zentrum Berlin für Materialien und Energie（柏林亥姆霍兹材料与能源中心）；European Synchrotron Radiation Facility（欧洲同步辐射装置）；Karlsruhe Institute of Technology (KIT)（卡尔斯鲁厄理工学院）
Muon spin relaxation measurements are reported on samples of dimethylammonium metal formates containing magnetic divalent nickel, cobalt, manganese, and copper ions. These hybrid organic-inorganic perovskites exhibit weak ferromagnetism and are, apart from the copper system, multiferroics with well separated magnetic and antiferroelectric transitions. We use muons to follow the sublattice magnetization, observing the effect of the spin reorientation transitions below TN and the criticality approaching TN. The multiferroic samples have three-dimensional antiferromagnetic interactions, but the c…
We show that the symmetry of the spin zigzag chain E phase of the orthorhombic perovskite manganites and nickelates allows for the existence of a finite ferroelectric polarization. The proposed microscopic mechanism is independent of spin-orbit coupling. We predict that the polarization induced by the E-type magnetic order can potentially be enhanced by up to two orders of magnitude with respect to that in the spiral magnetic phases of TbMnO3 and similar multiferroic compounds.
The recent discovery nickel oxides superconductors have highlighted the importance of first-principles simulations for understanding the formation of the bound electrons at the core of superconductivity. Nevertheless, superconductivity in oxides is often ascribed to strong electronic correlation effects that Density Functional Theory (DFT) cannot properly take into account, thereby disqualifying this technique. Being isostructural to nickel oxides, Sr1-xKxBiO3 superconductors form an ideal testbed for unveiling (i) the lowest theory level needed to model complex superconductors and (ii) the un…
Motivated by the nickel valence controversy in the perovskite nickelate RNiO_3, we consider a one-dimensional underscreened Kondo chain consisting of alternating spin-1 ("nickel") and electron ("oxygen") sites, which in addition to the usual electron hopping and spin-spin interaction between the S=1 spin and the electron also contains a spin mediated electron hopping term. Using the density-matrix renormalization group (DMRG), we obtained the zero temperature phase diagram of the model, as well as various correlation functions in each phase. Importantly, for a certain range of parameters the m…
We have investigated cobaltite relatives of the layered perovskite cuprates and nickelates, Pr$_{2-x}$Ca$_x$CoO$_4$ ($0.39 \leq x \leq 0.73$) and La$_{2-x}$Sr$_x$CoO$_4$ ($x = 0.61$), using elastic neutron scattering. We have discovered doping-dependent incommensurate short-range ordering of charges and magnetic moments, which in cobaltites occur in the range of heavy doping, $ 0.5 \lesssim x \lesssim 0.75$. The charge order exists already at room temperature and shows no change on cooling. The incommensurability of its propagation vector, ${\bf Q}_c = (ε_c,0,l)$, roughly scales with the conce…
The effect of cobalt and nickel substitutions for manganese on the physical properties of the perovskite manganite La1.2Bi0.8Mn2-x(Ni/Co)xO6+d, with x = 0.0-0.8, has been investigated. It is observed that the ferromagnetism is enhanced, TC being increased from 103 K for the parent compound (x = 0.0) to 178 K for Ni-phase, and to 181 K for the Co-phase (x = 0.8). Moreover, the systems remain insulating and depict relatively large values of magnetoresistance effect at low temperatures (up to 67 % at 90K and 70 kOe, for x = 0.0 phase). These phenomena are interpreted by means of electronic phase …
We study numerically the one-dimensional ferromagnetic Kondo lattice. This model is widely used to describe nickel and manganese perovskites. Due to the competition between double and super-exchange, we find a region where the formation of magnetic polarons induces a charge-ordered state. This ordering is present even in the absence of any inter-site Coulomb repulsion. There is an insulating gap associated to the charge structure formation. We also study the insulator-metal transition induced by a magnetic field which removes simultaneously both charge and spin ordering.
The existence of band gaps in Mott insulators such as perovskite oxides with partially filled 3d shells has been traditionally explained in terms of strong, dynamic inter-electronic repulsion codified by the on-site repulsion energy U in the Hubbard Hamiltonian. The success of the "DFT+U approach" where an empirical on-site potential term U is added to the exchange-and correlation Density Functional Theory (DFT) raised questions on whether U in DFT+U represents interelectronic correlation in the same way as it does in the Hubbard Hamiltonian, and if empiricism in selecting U can be avoided. He…
Dynamical mean field theory calculations are used to show that for late transition-metal-oxides a critical variable for the Mott/charge-transfer transition is the number of d-electrons, which is determined by charge transfer from oxygen ions. Insulating behavior is found only for a narrow range of d-occupancy, irrespective of the size of the intra-d Coulomb repulsion. The result is useful in interpreting 'density functional +U' and 'density functional plus dynamical mean field' methods in which additional correlations are applied to a specific set of orbitals and an important role is played by…
