Origin of band gaps in 3d perovskite oxides

Varignon, Julien; Bibès, Manuel; Zunger, Alex

doi:10.1038/s41467-019-09698-6

Cited by 189 publications

(168 citation statements)

References 74 publications

(139 reference statements)

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“…The discussion on polymorphous networks in cubic halide perovskites focuses on positional polymorphism. There is also spin polymorphism (ie different local spin environments) noted earlier for electronic spin in paramagnetic 3d oxide 60,61 and in the paraelectric electronic polarization 62,63 . The polymorphous cubic phases apply also to oxides that have dynamically unstable phonons, as shown in Fig.…”

Section: Not Only In Halide Perovskitesmentioning

confidence: 63%

Polymorphous nature of cubic halide perovskites

et al. 2020

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It has been long known that numerous halide and oxide perovskites can have non-ideal octahedra, showing tilting, rotation, and metal atom displacements. It has also been known that compounds that have at low temperatures a single structural motif ("monomorphous structures") could become disordered at higher temperatures, resulting in non-ideal octahedra as an entropy effect. What is shown here is that in many cubic halide perovskites and some oxides compounds a distribution of different low-symmetry octahedra ("polymorphous networks") emerge already from the minimization of the systems internal energy, i.e., they represent the intrinsic, preferred low temperature pattern of chemical bonding. Thermal disorder effects build up at elevated temperatures on top of such low temperature polymorphous networks. Compared with the monomorphous counterparts, the polymorphous networks have lower predicted total energies (enhanced stability), larger band gaps and dielectric constants now dominated by the ionic part, and agrees much more closely with the observed pair distribution functions. The nominal cubic perovskites (Pm-3m) structure deduced from X-Ray diffraction is actually a macroscopically averaged, high symmetry configuration, which should not be used to model electronic properties, given that the latter reflect a low symmetry local configuration.

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Section: Not Only In Halide Perovskitesmentioning

confidence: 63%

Polymorphous nature of cubic halide perovskites

et al. 2020

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“…(h) JT distortions as well as semiclassical size effect distortions can contribute to the opening of band gaps in Mott insulators. We have previously identified 33 We conclude that the electronically-induced Jahn-Teller distortion mode Q2and the geometrically induced steric Q2 + octahedral deformation mode are fully captured by a static mean-field method. This is in line with recent theoretical works that have demonstrated that static mean-field methods capable of inducing broken symmetry such as Density Functional Theory 13,26,30,33 in a polymorphous representation suffice to also explain (i) the trends in gapping and type of magnetic order across the ternary ABO3 series 33…”

Section: A Landau-esque Perturbation Approachmentioning

confidence: 65%

Origins versus fingerprints of the Jahn-Teller effect in d -electron ABX3 perovskites

Varignon

Bibès

Zunger

2019

Phys. Rev. Research

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The Jahn-Teller (JT) distortion that can remove electronic degeneracies in partially occupied states and results in systematic atomic displacements is a common underlying feature to many of the intriguing phenomena observed in 3d perovskites, encompassing magnetism, superconductivity, orbital ordering and colossal magnetoresistance. Although the seminal Jahn and Teller theorem has been postulated almost a century ago, the origins of this effect in perovskite materials are still debated, including propositions such as super exchange, spin-phonon coupling, sterically induced lattice distortions, and strong dynamical correlation effects. Although the end-result of JT distortions often include a mix of such various contributions, due to coupling of various lattice, spin, and electronic modes with the distortions ("fingerprints", or "consequences" of JT), it is not clear what is the primary cause: Which cases are caused by a pure electronic instability associated with degeneracy removal, as implied in the Jahn-Teller theorem, and which cases originate from other causes, such as semiclassical size effects. Here, we inquire about the origin and predictability of different types of octahedral deformation by using a Landau-esque approach, where the orbital occupation pattern of a symmetric structure is perturbed, finding if it is prone to total-energy lowering electronic instability or not. This is done for a systematic series of ABX3 perovskite compounds having 3d orbital degeneracies, using the density functional approach. We identify (i) systems prone to an electronicinstability (a true JT effect), such as KCrF3, KCuF3, LaVO3, KFeF3 and KCoF3, where the instability is independent of magnetic order, and forces a specific orbital-arrangement that is accommodated by a BX6 octahedral deformation with a specific symmetry. On the other hand, (ii) compounds such as LaTiO3 and LaMnO3 with delocalized d states do not show any electronically driven instability. Here, their octahedral deformation mode results from coupling of lattice mode with semiclassical sizeeffects (sterically induced), such as BX6 octahedra rotations. (iii) Although RVO3 (R=Lu-La, Y) perovskites exhibit similar hybridizations as LaTiO3, their t2g 2 electronic structure is highly unstable and ABX3 (X=O, F) perovskites 1,2 show a number of systematic atomic distortions relative to the ideal cubic perovskite structure: the one made of corner-sharing, vertically positioned, all parallel BX6 octahedra with equal B-X bonds. The interpretation of much of the electronic and magnetic phenomenology surrounding such perovskites 1,2 , including superconductivity, colossal magnetoresistance, orbital ordering and metal-insulator transitions is intimately related to the understanding of the causes vs. consequences of the observed atomic distortions. Usually, distortion in ABX3 perovskites produce inequivalent B-X bonds length, such as the Q2 motion (cf. Figure 2 of Ref. 3 ) that differentiate bond length along the x and y directions. These exist either as in-phase motions ...

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“…52 In line with this result, recent SCAN-based studies obtain band gaps in the high-temperature cuprates and 3d transition-metal perovskite oxides in accord with experimental observations. 37,38,40,53 This enables us to avoid the GW quasiparticle corrections and use directly the generalized Kohn-Sham band energies as the eigenvalues of the electrons (E ck+Q ) and holes (E vk ) in the BSE Hamiltonian, where only seven conduction and seven valence bands were considered. Figure 1(a) and 1(c) show the electronic band structure (blue lines) and crystal structure of La 2 CuO 4 in the LTO structure for the antiferromagnetic (AFM) phase.…”

Section: Computational Methodologymentioning

confidence: 99%

Landscape of coexisting excitonic states in the insulating single-layer cuprates and nickelates

Zhu

2020

Phys. Rev. B

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We present an ab initio study of the excitonic states of a prototypical high-temperature superconductor La2CuO4 and compare them to the isostructural single-layer nickelate La2NiO4. Key difference in the low-energy electronic structure leads to very different excitonic behavior. Excitons in La2CuO4 are delocalized and can freely move in the CuO2 plane without disturbing the antiferromagnetic order. In contrast, in La2NiO4 we find the low-lying excitonic states to be extremely localized, producing a nearly flat dispersion. The theoretically obtained excitonic dispersion and behavior are in excellent agreement with RIXS observations. To classify the excitons we project the electron-hole coupling onto each atomic site including the full manifold of atomic orbitals. We find the excitons to be composed of a linear combination of exciton classes, including Mott-Hubbard, d − d, and charge-transfer. The implication of these excitations to the high-Tc pairing mechanism is also discussed. arXiv:2003.00098v1 [cond-mat.str-el]

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Origin of band gaps in 3d perovskite oxides

Cited by 189 publications

References 74 publications

Polymorphous nature of cubic halide perovskites

Polymorphous nature of cubic halide perovskites

Origins versus fingerprints of the Jahn-Teller effect in d -electron ABX3 perovskites

Landscape of coexisting excitonic states in the insulating single-layer cuprates and nickelates

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