arXiv subjects

L. Chioncel

Publications and source records attributed to L. Chioncel.

63 records · Page 4Linked to original sources

arXiv2005

Observation and theoretical description of the pure Fano-effect in the valence-band photo-emission of ferromagnets

The pure Fano-effect in angle-integrated valence-band photo-emission of ferromagnets has been observed for the first time. A contribution of the intrinsic spin polarization to the spin polarization of the photo-electrons has been avoided by an appropriate choice of the experimental parameters. The theoretical description of the resulting spectra reveals a complete analogy to the Fano-effect observed before for paramagnetic transition metals. While the theoretical photo-current and spin difference spectra are found in good quantitative agreement with experiment in the case of Fe and Co only a qualitative agreement could be achieved in the case of Ni by calculations on the basis of plain local spin density approximation (LSDA). Agreement with experimental data could be improved in this case in a very substantial way by a treatment of correlation effects on the basis of dynamical mean field theory (DMFT).

cond-mat.str-el↗

arXiv2005

Multiple scattering formalism for correlated systems: A KKR+DMFT approach

We present a charge and self-energy self-consistent computational scheme for correlated systems based on the Korringa-Kohn-Rostoker (KKR) multiple scattering theory with the many-body effects described by the means of dynamical mean field theory (DMFT). The corresponding local multi-orbital and energy dependent self-energy is included into the set of radial differential equations for the single-site wave functions. The KKR Green's function is written in terms of the multiple scattering path operator, the later one being evaluated using the single-site solution for the $t$-matrix that in turn is determined by the wave functions. An appealing feature of this approach is that it allows to consider local quantum and disorder fluctuations on the same footing. Within the Coherent Potential Approximation (CPA) the correlated atoms are placed into a combined effective medium determined by the dynamical mean field theory (DMFT) self-consistency condition. Results of corresponding calculations for pure Fe, Ni and Fe$_{x}$Ni$_{1-x}$ alloys are presented.

cond-mat.str-el↗

arXiv2005

Tunable spin transport in CrAs: role of correlation effects

Correlation effects on the electronic structure of half-metallic CrAs in zinc-blende structure are studied for different substrate lattice constants. Depending on the substrate the spectral weight of the non-quasiparticle states might be tuned from a well developed value in the case of InAs substrate to an almost negligible contribution for the GaAs one. A piezoelectric material that would allow the change in the substrate lattice parameters opens the possibility for practical investigations of the switchable (tunable) non-quasiparticle states. Since the latter are important for the tunneling magnetoresistance and related phenomena it creates new opportunities in spintronics.

cond-mat.str-el↗

arXiv2004

Correlation effects in Co/Cu and Fe/Cr magnetic multilayers

The electronic structure of Co/Cu(001) and Fe/Cr(001) magnetic multilayers has been investigated within the local density approximation combined with dynamical mean field theory. Our calculation shows enhanced density of states at the Fermi level, suggesting that electronic correlations might play an important role in the transport properties of multilayers.

cond-mat.str-el↗

arXiv2004

Ab-initio calculations of the optical and magneto-optical properties of moderately correlated systems: accounting for correlation effects

The influence of dynamical correlation effects on the magneto-optical properties of ferromagnetic Fe and Ni has been investigated. In addition the temperature dependence of the self-energy and its influence on the DOS and optical conductivity is considered. Magneto-optical properties were calculated on the basis of the one-particle Green's function, which was obtained from the DMFT-SPTF procedure. It is shown that dynamical correlations play a rather important role in weakly correlated Fe and substantially change the spectra for moderately correlated Ni. Magneto-optical properties obtained for both systems are found in better agreement with experiment than by conventional LDA calculations.

cond-mat.str-el↗

arXiv2004

On the effect of short-range magnetic ordering on electron energy-loss spectra in spinels

The energy-loss near-edge structure (ELNES) at the oxygen $K$ edge in two $AB_2O_4$ spinels (A=Mg, B=Al,Cr) is reported. In $MgAl_2O_4$ the experimental data is successfully modelled within the LDA framework. In the case of $MgCr_2O_4$ spin-polarisation, in the form of antiferromagnetic ordering on the Cr sub-lattice, must be included despite the fact that the measurements were performed at approximately 30 times above $T_N$. A model in which dynamic short-range antiferromagnetic ordering is present at room temperature is proposed to explain the results of the experiments and calculations.

cond-mat.mtrl-sci↗

arXiv2003

Nonquasiparticle states in half-metallic ferromagnet NiMnSb

Nonquasiparticle states above the Fermi energy are studied by first-principle dynamical mean field calculations for a prototype half-metallic ferromagnet, NiMnSb. We present a quantitative evaluation of the spectral weight of this characteristic feature and discuss the possible experimental investigation (BIS, NMR, STM and Andreev reflection) to clarify the existence of these states.

cond-mat.str-el↗

arXiv2003

Ab initio electronic structure calculation of correlated systems: EMTO-DMFT approach

We propose a self-consistent method for electronic structure calculations of correlated systems, which combines the local spin-density approximation (LSDA) and the dynamical mean field theory (DMFT). The LSDA part is based on the exact muffin-tin orbital approach, meanwhile the DMFT uses a perturbation scheme that includes the T matrix with fluctuation exchange approximation. The current LSDA+DMFT implementation fulfills both self-energy and charge self-consistency requirements. We present results on the electronic structure calculations for bulk 3d transition metals (Cr, Fe, and Ni) and for Fe/Cr magnetic multilayers. The latter demonstrates the importance of the correlation effects for the properties of magnetic heterostructures.

cond-mat.str-el↗

arXiv2002

Correlated metals and the LDA+U method

While LDA+U method is well established for strongly correlated materials with well localized orbitals, its application to weakly correlated metals is questionable. By extending the LDA Stoner approach onto LDA+U, we show that LDA+U enhances the Stoner factor, while reducing the density of states. Arguably the most important correlation effects in metals, fluctuation-induced mass renormalization and suppression of the Stoner factor, are missing from LDA+U. On the other hand, for {\it moderately} correlated metals LDA+U may be useful. With this in mind, we derive a new version of LDA+U that is consistent with the Hohenberg-Kohn theorem and can be formulated as a constrained density functional theory. We illustrate all of the above on concrete examples, including the controversial case of magnetism in FeAl.

cond-mat.str-el↗