As silicon is the basis of conventional electronics, so strontium titanate (SrTiO(3)) is the foundation of the emerging field of oxide electronics. SrTiO(3) is the preferred template for the creation of exotic, two-dimensional (2D) phases of electron matter at oxide interfaces that have metal-insulator transitions, superconductivity or large negative magnetoresistance. However, the physical nature of the electronic structure underlying these 2D electron gases (2DEGs), which is crucial to understanding their remarkable properties, remains elusive. Here we show, using angle-resolved photoemission spectroscopy, that there is a highly metallic universal 2DEG at the vacuum-cleaved surface of SrTiO(3) (including the non-doped insulating material) independently of bulk carrier densities over more than seven decades. This 2DEG is confined within a region of about five unit cells and has a sheet carrier density of ∼0.33 electrons per square lattice parameter. The electronic structure consists of multiple subbands of heavy and light electrons. The similarity of this 2DEG to those reported in SrTiO(3)-based heterostructures and field-effect transistors suggests that different forms of electron confinement at the surface of SrTiO(3) lead to essentially the same 2DEG. Our discovery provides a model system for the study of the electronic structure of 2DEGs in SrTiO(3)-based devices and a novel means of generating 2DEGs at the surfaces of transition-metal oxides.

We introduce a model that accounts for the bipolar resistive switching phenomenom observed in transition metal oxides. It qualitatively describes the electric field-enhanced migration of oxygen vacancies at the nano-scale. The numerical study of the model predicts that strong electric fields develop in the highly resistive dielectric-electrode interfaces, leading to a spatially inhomogeneous oxygen vacancies distribution and a concomitant resistive switching effect. The theoretical results qualitatively reproduce non-trivial resistance hysteresis experiments that we also report, providing key validation to our model.

We have synthesized for the first time the metastable compound 1T-CrTe2. We have done its complete structural characterization and measured its magnetization, specific heat and electrical resistivity between 4 and 330 K. We have also performed detailed band structure calculations. We have found that it crystallizes in the CdI2 structure type and that its electrical resistance follows a metallic behaviour below room temperature. Its magnetization and specific heat curves show that the compound has a transition to a ferromagnetic state at TC = 310 K, with the magnetic moments ordered parallel to the basal plane. From the specific heat measurements and the ferromagnetic solutions obtained from our DFT calculations, we conclude that the ferromagnetism is of itinerant nature.

An unusual quasi-two-dimensional heavy band mass van Hove singularity (vHs) lies very near the Fermi energy in MgCNi3, recently reported to superconduct at 8.5 K. This compound is strongly exchange enhanced and unstable to ferromagnetism upon hole doping with approximately 12% Mg-->Na or Li (i.e., 0.04 hole/Ni). We identify an essentially infinite mass along the M-Gamma line, which accounts for the two dimensionality of this vHs. This compound provides new opportunities to probe the ferromagnetic critical point as well as introducing the novelties of 2D behavior into a 3D system.