Spin state transition and covalent bonding in LaCoO3

We use the dynamical mean-field theory to study a p-d Hubbard Hamiltonian for LaCoO3 derived from ab initio calculations in local density approximation (LDA+DMFT scheme). We address the origin of local moments observed above 100 K and discuss their attribution to a particular atomic multiplet in the presence of covalent Co-O bonding. We show that in solids such attribution, based on the single ion picture, is in general not possible. We explain when and how the single ion picture can be generalized to provide a useful approximation in solids. Our results demonstrate that the apparent magnitude of the local moment is not necessarily indicative of the underlying atomic multiplet. We conclude that the local moment behavior in LaCoO3 arises from the high-spin state of Co and explain the precise meaning of this statement

Spin state of negative charge-transfer material SrCoO3

We employ the combination of the density functional and the dynamical mean-field theory (LDA+DMFT) to investigate the electronic structure and magnetic properties of SrCoO3, monocrystal of which were prepared recently. Our calculations lead to a ferromagnetic metal in agreement with experiment. We find that, contrary to some suggestions, the local moment in SrCoO3 does not arise from intermediate spin state, but is a result of coherent superposition of many different atomic states. We discuss how attribution of magnetic response to different atomic states in solids with local moments can be quantified.Comment: 5 pages, 5 figure

Lateral elongation of InAs/GaAs quantum dots studied by magnetophotoluminescence

We have investigated single layer InAs QDs on GaAs substrate grown by MOVPE by means of magnetophotoluminescence up to 24 T. Fitting the field-dependence of band positions, we have found the ratio of lateral sizes within 1.5 –1.7, and the effective mass of 0.04 – 0.05

Type-I and Type-II Confinement in Quantum Dots: Excitonic Fine Structure

We have theoretically studied type-I and type-II confinement in InAs quantum dots with GaAs_{1-y}Sb_y capping layer. The character of the confinement can be adjusted by the Sb content. We have found that upon the transition from type-I to type-II confinement the hole wave functions change the topology from a compact shape to a two-segment shape, resulting in the complex changes in the exciton fine structure splitting with zero values at narticular compositions. Additionally, a high exciton radiative recombination probability is preserved even in type-II. This allows to design strongly luminescent quantum dots with naturally low fine structure splitting, which could serve as sources of entangled photon pairs for quantum communication

Determination of Quantum Dot Morphology from Magnetooptical Properties

We present here the calculations of magnetooptical properties in InAs/GaAs quantum dots with different shapes, including excitonic effects. The influence of several structural parameters, such as vertical profile, aspect ratio, and basis squareness is discussed, as well as the possibility to retrieve the structural parameters from magnetooptical measurements

Modeling of plasmon-enhanced photoluminescence of Si nanocrystals embedded in thin silicon-rich oxinitride layer

Plasmon-enhanced photoluminescence of silicon nanocrystals embedded in silicon-rich oxinitride thin film is calculated using finite-difference time-domain simulations. Emitters are represented as point-like dipoles and the photoluminescence enhancement is calculated depending on the emitter's position and polarization with respect to the plasmonic metal nanoparticle placed on top of the layer. We show that the photoluminescence enhancement is dominated by the excitation enhancement even for tuning the metal nanoparticle size to the emission wavelength