12,755 research outputs found
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
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