Abstract With their broad range of properties, ABO 3 transition metal perovskite oxides have long served as a platform for device applications and testing bed different condensed matter theories. Their insulating character structural distortions are often ascribed to dynamical electronic correlations within universal, symmetry-conserving paradigm. This view restricts predictive theory complex computational schemes, going beyond density functional (DFT). Here, we show that, if one allows...

The properties of AMO3 perovskite oxides, where M is a 3d transition metal, depend strongly on the level covalency between metal d and oxygen p orbitals. With their complex spin orders metal-insulator transition, rare-earth nickelates verge dominantly ionic covalent characters. Accordingly, nature ground state highly debated. Here, we reconcile visions insulating nickelates. Through first-principles calculations, show that it reminiscent charge disproportionation picture (with strictly...

Abstract In magnetic materials, the Pauli exclusion principle typically drives anti-alignment between electron spins on neighbouring species resulting in antiferromagnetic behaviour. Ferromagnetism exhibiting spontaneous spin alignment is a fairly rare behaviour, but once materialized often associated with itinerant electrons metals. Here we predict and rationalize robust ferromagnetism an insulating oxide perovskite structure based popular titanate series. half-doped layered titanates,...

The existence of band gaps in Mott insulators such as perovskite oxides with partially filled 3d shells has been traditionally explained terms strong, dynamic inter-electronic repulsion codified by the on-site energy U Hubbard Hamiltonian. success "DFT+U approach" where an empirical potential term is added to exchange-and correlation Density Functional Theory (DFT) raised questions on whether DFT+U represents interelectronic same way it does Hamiltonian, and if empiricism selecting can be...

Through CaH2 chemical reduction of a parent R3+Ni3+O3 perovskite form, superconductivity was recently achieved in Sr-doped NdNiO2 on SrTiO3 substrate. Using density functional theory (DFT) calculations, we find that stoichiometric is significantly unstable with respect to decomposition into 1/2[Nd2O3 + NiO Ni] exothermic energy +176 meV/atom, considerably higher instability than for common ternary oxides. This poses the question if nickelate compound used extensively model electronic band...

Abstract Perovskite oxides are already widely used in industry and have huge potential for novel device applications thanks to the rich physical behaviour displayed these materials. The key functional electronic properties exhibited by perovskites is often so-called Jahn-Teller distortion. For applications, an electrical control of distortions, which so far out reach, would therefore be highly desirable. Based on universal symmetry arguments, we determine new lattice mode couplings that can...

Some $AB{X}_{3}$ perovskites exhibit different local environments (DLE) for the same $B$ atoms in lattice, an effect referred to as disproportionation, distinguishing such compounds from common that have single (SLE). The basic phenomenology associated with disproportionation involves absence of $B$-atom charge ordering, creation B-X bond length (``bond alternation'') environments, appearance metal (in SLE) insulator DLE) transitions, and formation ligand holes. We point out this is a broad...

The authors identify the modalities enabling an electronically induced distortion, which is identical across board of 3d elements showing electronic degenerate states in high symmetry cubic cell. This constitutes fingerprint a Jahn-Teller effect. Materials without instabilities such as LaMnO3 display alternate lattice distortion simply resulting from mode couplings with sterically distortions.

The Jahn-Teller distortion, by its very nature, is often at the heart of various electronic properties displayed perovskites and related materials. Despite mode being nonpolar, we devise demonstrate, in present Letter, an electric field control distortions bulk perovskites. enabled through anharmonic lattice coupling between distortion a polar mode. We confirm this quantify it first-principles calculations. will always exist within Pb2_{1}m space group, which found to be favored ground state...

In transition metal perovskites (ABO3) most physical properties are tunable by structural parameters such as the rotation of BO6 octahedra. Examples include N\'eel temperature orthoferrites, conductivity mixed-valence manganites, or band gap rare-earth scandates. Since oxides often host large internal electric dipoles and can accommodate heavy elements, they also emerge prime candidates to display Rashba spin-orbit coupling, through which charge spin currents may be efficiently...

Gray tin, also known as $\ensuremath{\alpha}$-Sn, can be turned into a three-dimensional topological insulator (3D-TI) by strain and finite-size effects. Such room-temperature 3D-TI is peculiarly interesting for spintronics due to the spin-momentum locking along Dirac cone (linear dispersion) of surface states. Angle-resolved photoemission spectroscopy (ARPES) has been used investigate dispersion close Fermi level in thin (001)-oriented epitaxially strained films $\ensuremath{\alpha}$-Sn...

Abstract The recent discovery of nickel oxide superconductors have highlighted the importance first-principles simulations for understanding formation bound electrons at core 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 oxides, Sr 1-x K x BiO 3 form an ideal testbed unveiling lowest level...

Using first-principles calculations, we study theoretically the stable $2H$ hexagonal structure of BaMnO${}_{3}$. We show that from high-temperature $P{6}_{3}/mmc$ structure, compound should exhibit an improper ferroelectric structural phase transition to a $P{6}_{3}cm$ ground state. Combined with its antiferromagnetic properties, $2H$-BaMnO${}_{3}$ is therefore expected be multiferroic at low temperature. The mechanism in ${\mathrm{BaMnO}}_{3}$ appears similar what was reported YMnO${}_{3}$...

Rare-earth titanates ${\mathrm{RTiO}}_{3}$ are Mott insulators displaying a rich physical behavior, featuring most notably orbital and spin orders in their ground state. The origin of ferromagnetic to antiferromagnetic transition as function the size rare earth however remains debated. Here we show on basis symmetry analysis first-principles calculations that although rare-earth nominally Jahn-Teller active, distortion is negligible irrelevant for description state properties. At same time,...

Transition metal oxides having a perovskite structure form wide and technologically important class of compounds. In these systems, ferroelectric, ferromagnetic, ferroelastic, or even orbital charge orderings can develop eventually coexist. These be tuned by external electric, magnetic, stress field, the cross-couplings between them enable multifunctional properties, such as piezoelectricity, magneto-electricity, magneto-elasticity. Recently, it has been proposed that additional to typical...

The Rashba parameter ${\ensuremath{\alpha}}_{R}$ is usually assumed to scale linearly with the amplitude of polar displacements by construction spin-orbit interaction. On basis first-principles simulations, ferroelectric phases ${\mathrm{SrTiO}}_{3}$ reached under epitaxial compressive strain are characterized (i) large effects at bottom conduction band near paraelectric-ferroelectric boundary and (ii) an unexpected suppression phenomena when increases. This peculiar behavior ascribed...

Superconductivity is one of the most intriguing properties matter, described by an attractive interaction that binds electrons into Cooper pairs. To date, highest critical temperature at ambient conditions achieved in copper oxides. While layered nickel oxides were long proposed to be analogous cuprates, superconductivity was only demonstrated 2019 albeit without clarifying pairing mechanism. Here we use density functional theory show nickelates driven electron-phonon coupling originating...

Several materials transition from an insulating to a superconducting state by reducing the strength of electron-phonon coupling associated with charge and bond orderings provided that remains strong enough produce Cooper pairs. While Jahn-Teller effect is at core producing states orbital orderings, its implication in superconductivity unobserved. Here, parameter-free first-principles calculations, we reveal A2RuO4 (A = Sr, Ca) emerges due mechanism proximity bond-ordered phase. The model...

Density functional theory (DFT) is one of the main tools for studying electronic structure solids and molecules. Nevertheless, drawbacks implementation DFT so-called self-interaction error (SIE) that can yield undesired delocalization errors ultimately results in prediction metals instead experimentally observed insulators. These SIEs be amended by using more evolved exchange-correlation functionals than standard local density approximation such as recent meta-generalized gradient strongly...

We measured the temperature-dependent infrared reflectivity spectra of ${\text{MnF}}_{2}$ between 4 and 600 K. show that phonon spectrum undergoes a clear renormalization at ${T}_{N}$. The ab initio calculation we performed on this compound accurately predicts magnitude direction changes in parameters across antiferromagnetic transition, showing they are mainly induced by magnetic order. In material, found dielectric constant is mostly from origin. large change lattice with temperature seen...

Rare-earth nickelates ${R}^{3+}{\mathrm{Ni}}^{3+}{\mathrm{O}}_{3}$ ($R=\mathrm{Lu}\text{\ensuremath{-}}\mathrm{Pr}$, 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 parent phases of newly identified infinite layer $R\mathrm{Ni}{\mathrm{O}}_{2}$ superconductors. Although intensive theoretical works have been devoted to understand origin bulk, there only few studies on role hole and electron...