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Three-dimensional BÍ2Te2Se topological insulator (TI) reveals itinerant-localized duality of correlated electrons. Motivated thereby, we investigate the role of local, multiorbital electron interactions in bulk BÍ2Te2Se. Within local density approximation plus dynamical mean-field theory (LDA + DMFT), we derive a Kondo-Mott electronic transition with an intermediate Dirac-like phase characterized by linear spectral functions. Mott localization and spin-orbit induced weak antilocalization mark the channel-selective insulating phase. Good semiquantitative agreement with spectroscopy and electrical transport can serve as a theoretical basis for postulating that Mottness is a remarkable way to approach maximally bulk-insulating behavior in real Tis. [ABSTRACT FROM AUTHOR]

We report on bulk electronic structure and transport properties of pure and doped Bi2Se3 topological insulators. Using the local-density approximation plus dynamical mean-field theory for the real multiorbital case, we propose a new scenario in which Bi2Se3 is a selective, multiorbital Kondo system. We derive a filling-controlled metal-to-insulator crossover in this p-band material, predicting a continuous transition to a bulk Kondo insulator upon hole doping. By explicitly including the spin-orbit interaction, good semiquantitative agreement with effective mass and spectral and dc transport responses is obtained. This serves as a theoretical basis for postulating that Bi2Se3 is a sizable correlated electron system close to electronic (or topological) transitions. [ABSTRACT FROM AUTHOR]

The newly discovered 122-iron-chalcogenide superconductors show clear signatures of Mott-insulating and strange, incoherent metal normal states. Motivated thereby, we use local-density approximation plus dynamical mean-field theory (LDA + DMFT) to study the electronic structure and transport properties of KxFe2-ySe2. We find that the undoped KFe1.6Se2 system is a new kind of Mott-Kondo insulator (MKI). Electron doping this MKI drives a Mott transition to an orbital-selective non-Fermi-liquid metal. Good agreement with spectral and transport responses supports our view, implying that superconductivity arises from a doped Mott insulator, as in the high-Tc cuprates. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the interplay between lattice distortion, bond formation and orbital ordering in (, Y) perovskites using full-potential density-functional calculations and ELF analysis. It is shown that the lattice distortion implies a dramatic reorganization of the bonds between A cations and oxygen on the one hand, and titanium and oxygen on the other hand. Along the series cubic LaTiO3, orthorhombic LaTiO3, orthorhombic YTiO3 an increasing asymmetrization of the environment of Ti is taking place. We show that changes in chemical bonding are relevant for lifting the degeneracy of Ti 3d orbitals across the metal–insulator transition and we sketch the use of the ELF to visualize orbital ordering. [Copyright &y& Elsevier]

Unusual metallic states involving breakdown of the standard Fermi-liquid picture of long-lived quasiparticles in well-defined band states emerge at low temperatures near correlation-driven Mott transitions. Prominent examples are ill-understood metallic states in d- and f-band compounds near Mott-like transitions. Finding of superconductivity in solid O 2 on the border of an insulator-metal transition at high pressures close to 96 GPa is thus truly remarkable. Neither the insulator-metal transition nor superconductivity are understood satisfactorily. Here, we undertake a first step in this direction by focussing on the pressure-driven insulator-metal transition using a combination of first-principles density-functional and many-body calculations. We report a striking result: the finding of an orbital-selective Mott transition in a pure p-band elemental system. We apply our theory to understand extant structural and transport data across the transition, and make a specific two-fluid prediction that is open to future test. Based thereupon, we propose a novel scenario where soft multiband modes built from microscopically coexisting itinerant and localized electronic states are natural candidates for the pairing glue in pressurized O 2 .

Transport properties of tetragonal iron monosulfide, mackinawite, show a range of complex features. Semiconductive behavior and proximity to metallic states with nodal superconductivity mark this d-band system as unconventional quantum material. Here, we use the density functional dynamical mean-field theory (DFDMFT) scheme to comprehensively explain why tetragonal FeS shows both semiconducting and metallic responses in contrast to tetragonal FeSe which is a pseudogaped metal above the superconducting transition temperature. Within local-density-approximation plus dynamical mean-field theory (LDA+DMFT) we characterize its paramagnetic insulating and metallic phases, showing the proximity of mackinawite to selective Mott localization. We report the coexistence of pseudogaped and anisotropic Dirac-like electronic dispersion at the border of the Mott transition. These findings announce a new understanding of many-particle physics in quantum materials with coexisting Dirac-fermions and pseudogaped electronic states at low energies. Based on our results we propose that in electron-doped FeS substantial changes would be seen when the metallic regime was tuned towards an electronic state that hosts unconventional superconductivity.

Materials with strong spin-orbit coupling, which competes with other particle-particle interactions and external perturbations, offer a promising route to explore novel phases of quantum matter. Using LDA + DMFT we reveal the complex interplay between local, multi-orbital Coulomb and spin-orbit interaction in elemental bismuth. Our theory quantifies the role played by collective dynamical fluctuations in the spin-orbit Kondo state. The correlated electronic structure we derive is promising in the sense that it leads to results that might explain why moderate magnetic fields can generate Dirac valleys and directional-selective magnetoresistance responses within spin-orbit Kondo metals.

Motivated by a collection of experimental results indicating the strongly correlated nature of the ferromagnetic metallic state of CrO2, we present results based on a combination of the actual band structure with dynamical-mean-field theory for the multiorbital case. In striking contrast to LSDA(+U) and model many-body approaches, much better semiquantitative agreement with (i) recent photoemission results, (ii) domain of applicability of the half-metal concept, and (iii) thermodynamic and dc transport data is obtained within a single picture. Our approach has broad applications for the detailed first-principles investigation of other transition metal oxide-based half-metallic ferromagnets.