Andrey Titov

Momentum Distribution and Renormalization Factor in Sodium and the Electron Gas

We present experimental and theoretical results on the momentum distribution and the quasiparticle renormalization factor in sodium. From an x-ray Compton-profile measurement of the valence-electron-momentum density, we derive its discontinuity at the Fermi wave vector. This yields an accurate measure of the renormalization factor that we compare with quantum Monte Carlo and G0W0 calculations performed both on crystalline sodium and on the homogeneous electron gas.

Interface-driven phase separation in multifunctional materials: the case of GeMn ferromagnetic semiconductor

We use extensive first principle simulations to show the major role played by interfaces in the mechanism of phase separation observed in semiconductor multifunctional materials. We make an analogy with the precipitation sequence observed in over-saturated AlCu alloys, and replace the Guinier-Preston zones in this new context. A new class of materials, the

Momentum distribution and Compton profile by the ab initio GW approximation

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First-principles study of the new compounds CrGa2Sb2 and CrGaSb synthesized under high pressure

phases, is proposed to understand the formation of the coherent precipitates observed in the GeMn system. The interplay between formation and interface energies is analyzed for these phases and for the structures usually considered in the literature. The existence of the alpha phases is assessed with both theoretical and experimental arguments.

Determination of the optical constants of amorphous carbon in the EUV spectral region 40-450 eV

We present two possible approaches to calculate the momentum distribution n(p) and the Compton profile within the framework of the ab initio GW approximation on the self-energy. The approaches are based on integration of the Green’s function along either the real or the imaginary axes. Examples will be presented on the jellium model and on real bulk sodium. Advantages and drawbacks of both methods are discussed in comparison with accurate quantum Monte Carlo (QMC) calculations and x-ray Compton scattering experiments. We illustrate the effect of many-body correlations and disentangle them from band-structure and anisotropy effects by a comparison with density functional theory in the local density approximation. Our results suggest the use of G0W0 momentum distributions as reference for future experiments and theory developments.

X-ray magnetic circular dichroism in (Ge,Mn) compounds: experiments and modeling

We present the density-functional calculations of the compounds CrGa2Sb2 and CrGaSb synthesized recently under high pressure. Calculation reproduces well all details of the crystal structure of these compounds, their spin ordering, and a larger metallicity of CrGaSb comparing to CrGa2Sb2. Particular attention is given to the room temperature ferromagnetic compound CrGa2Sb2, where the huge resistivity hinting at the possible semiconducting properties was measured. To understand the mechanism of its anisotropic conductivity, we analyze the band structure, calculated kinetic and optical characteristics of this compound. It is found that the density of states of CrGa2Sb2 has a pseudogap near the Fermi level, where the Cr atoms do not dominate, but contribute even less than the atoms of Ga and Sb. This explains a very high calculated resistivity of CrGa2Sb2, which can be characterized as a ferromagnetic compound with a low metallic conductivity. This type of conductivity remains unchanged, when a possible Cr-deficiency of CrGa2Sb2 is taken into account or the MBJ-LDA exchange-correlation potential is used instead of the GGA-LDA one in calculation. The potential of this compound for the development of spintronic materials is discussed.

Ab Initio Calculation of the System Cr–GaSb: A New High-Pressure Phase Containing Defects

The extreme ultraviolet (EUV) optical constants δ(ω) and β(ω) of amorphous carbon were determined on the basis of transmission measurements at hω=18-450 eV, the first-principles calculation of the dielectric tensor at hω<25 eV, and the Kramers-Kronig calculation of δ(ω). Our optical constants generally agree with the CXRO data, excluding the vicinity of the K-edge. First-principles analysis shows that two thresholds of absorption (at 284 eV and 291 eV) found in the present study are caused, respectively, by the π- and σ- bonds. Their weights are controlled by an orientation of graphene sheets in a-carbon.

Ab Initio Study of Electronic and Magneto-Optical Properties of InSb:Mn and InAs:Mn

X-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectra at the L

Ab Initio Study of Electronic and Magnetic Properties of GaSb/Mn and GaAs/Mn Digital Ferromagnetic Heterostructures

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Properties of Ga1−xMnxN Epilayers Grown by Molecular Beam Epitaxy

edges of Mn in (Ge,Mn) compounds have been measured and are compared to the results of first principles calculation. Early \textit{ab initio} studies show that the Density Functional Theory (DFT) can very well describe the valence band electronic properties but fails to reproduce a characteristic change of sign in the L