Interface relaxation and electrostatic charge depletion in the oxide heterostructure LaAlO3/SrTiO3

Performing an analysis within density functional theory, we develop insight into the structural and electronic properties of the oxide heterostructure LaAlO3/SrTiO3. Electrostatic surface effects are decomposed from the internal lattice distortion in order to clarify their interplay. We first study the interface relaxation by a multi-layer system without surface, and the surface effects, separately, by a substrate-film system. While elongation of the TiO6 octahedra at the interface enhances the metallicity, reduction of the film thickness has the opposite effect due to a growing charge depletion. The interplay of these two effects, as reflected by the full lattice relaxation in the substrate-film system, however, strongly depends on the film thickness. An inversion of the TiO6 distortion pattern for films thinner than four LaAlO3 layers results in an insulating state.Comment: 10 pages, 7 figures, accepted by Europhysics Letter

Improved insertion-loss tester

An improved test method accurately measures the insertion loss of RF components while avoiding amplifier drift. Currents are balanced across a bridge transformer with shorted probes and then with each component to be tested. Differences in adjustments indicate the loss

Magnetic ground state of coupled edge-sharing CuO_2 spin-chains

By means of density functional theory, we investigate the magnetic ground state of edge-sharing CuO_2 spin-chains, as found in the (La,Ca,Sr)_14Cu_24O_41system, for instance. Our data rely on spin-polarized electronic structure calculations including onsite interaction (LDA+U) and an effective model for the interchain coupling. Strong doping dependence of the magnetic order is characteristic for edge-sharing CuO_2 spin-chains. We determine the ground state magnetic structure as function of the spin-chain filling and quantify the competing exchange interactions.Comment: 5 pages, 2 figures, 3 tables, accepted by Phys. Rev. Let

Insertion loss measuring apparatus having transformer means connected across a pair of bolometers Patent

High impedance alternating current sensing transformer device between two bolometers for measuring insertion loss of test componen