Oxygen vacancies and hydrogen doping in LaAlO/SrTiO heterostructures: electronic properties and impact on surface and interface reconstruction.

We investigate the effect of oxygen vacancies and hydrogen dopants at the surface and inside slabs of [Formula: see text], [Formula: see text], and [Formula: see text]/[Formula: see text] heterostructures on the electronic properties by means of electronic structure calculations as based on density functional theory. Depending on the concentration, the presence of these defects in a [Formula: see text] slab can suppress the surface conductivity. In contrast, in insulating [Formula: see text] slabs already very small concentrations of oxygen vacancies or hydrogen dopant atoms induce a finite occupation of the conduction band.

Unconventional aspects of electronic transport in delafossite oxides.

The electronic transport properties of the delafossite oxides [Formula: see text] are usually understood in terms of two well-separated entities, namely the triangular [Formula: see text] and ([Formula: see text] layers. Here, we review several cases among this extensive family of materials where the transport depends on the interlayer coupling and displays unconventional properties. We review the doped thermoelectrics based on [Formula: see text] and [Formula: see text], which show a high-temperature recovery of Fermi-liquid transport exponents, as well as the highly anisotropic metals [Formula: see text], [Formula: see text], and [Formula: see text], where the sheer simplicity of the Fermi surface leads to unconventional transport.

Pressure-Temperature Phase Diagram of Vanadium Dioxide.

The complexity of strongly correlated electron physics in vanadium dioxide is exemplified as its rich phase diagrams of all kinds, which in turn shed light on the mechanisms behind its various phase transitions. In this work, we map out the hydrostatic pressure-temperature phase diagram of vanadium dioxide nanobeams by independently varying pressure and temperature with a diamond anvil cell. In addition to the well-known insulating M1 (monoclinic) and metallic R (tetragonal) phases, the diagram identifies the existence at high pressures of the insulating M1' (monoclinic, more conductive than M1) phase and two metallic phases of X (monoclinic) and O (orthorhombic, at high temperature only).

Electronic properties of LaAlO/SrTiO n-type interfaces: a GGA+U study.

The role of electronic correlation effects for a realistic description of the electronic properties of [Formula: see text]/[Formula: see text] heterostructures as covered by the on-site Coulomb repulsion within the GGA+U approach is investigated. Performing a systematic variation of the values of the Coulomb parameters applied to the Ti 3d and La 4f orbitals we put previous suggestions to include a large value for the La 4f states into perspective. Furthermore, our calculations provide deeper insight into the band gap landscape in the space spanned by these Coulomb parameters and the resulting complex interference effects.

VO2: a novel view from band theory.

New calculations for vanadium dioxide, one of the most controversially discussed materials for decades, reveal that band theory as based on density functional theory is well capable of correctly describing the electronic and magnetic properties of the metallic as well as both the insulating M(1) and M(2) phases. Considerable progress in the understanding of the physics of VO(2) is achieved by the use of the recently developed hybrid functionals, which include part of the electron-electron interaction exactly and thereby improve on the weaknesses of semilocal exchange functionals as provided by the local density and generalized gradient approximations. Much better agreement with photoemission data as compared to previous calculations is found and a consistent description of the rutile-type early transition-metal dioxides is achieved.