Predicting the conductance of strongly correlated molecules: the Kondo effect in perchlorotriphenylmethyl/Au junctions.

Stable organic radicals integrated into molecular junctions represent a practical realization of the single-orbital Anderson impurity model. Motivated by recent experiments for perchlorotriphenylmethyl (PTM) molecules contacted to gold electrodes, we develop a method that combines density functional theory (DFT), quantum transport theory, numerical renormalization group (NRG) calculations and renormalized super-perturbation theory (rSPT) to compute both equilibrium and non-equilibrium properties of strongly correlated nanoscale systems at low temperatures effectively from first principles. We determine the possible atomic structures of the interfaces between the molecule and the electrodes, which allow us to estimate the Kondo temperature and the characteristic transport properties, which compare well with experiments. By using the non-equilibrium rSPT results we assess the range of validity of equilibrium DFT + NRG-based transmission calculations for the evaluation of the finite voltage conductance. The results demonstrate that our method can provide qualitative insights into the properties of molecular junctions when the molecule-metal contacts are amorphous or generally ill-defined, and that it can further give a fully quantitative description when the experimental contact structures are well characterized.

Magnetism and electronic structure calculation of SmN.

The results of the electronic structure calculations performed on SmN by using the LDA+U method with and without including the spin-orbit coupling are presented. Within the LDA+U approach, a N(2p) band polarization of about 0.3 µB is induced by Sm(4f)-N(2p) hybridization, and a half-metallic ground state is obtained. By including spin-orbit coupling the magnetic structure was shown to be antiferromagnetic of type II, with Sm spin and orbital moments nearly cancelling. This results into a semiconducting ground state, which is in agreement with experimental results.

On the R 5d band polarization in rare-earth-transition metal compounds.

Magnetic measurements and band structure calculations were performed on RT(2) and RT(5) compounds, where R is a heavy rare-earth and T = Fe, Co, Ni, Al, as well as on pseudobinary compounds GdCo(2 - x)A(x) (A = Ni, Cu, Si), YFe(2 - x)V(x) and YCo(4 - x)Ni(x)B. The calculated moments per formula unit described well the experimentally determined magnetizations. By considering the 4f-5d-3d exchange interactions, we evaluate the contributions of local 4f-5d and short range 5d-3d interactions to R 5d and Y 4d band polarizations. The 4f-5d induced polarizations are proportional to the De Gennes factor and are the same for a given R and a similar type structure. The R 5d and Y 4d band polarizations induced by R 5d-T3d or Y 4d-T3d hybridizations are proportional to the number of neighbouring T atoms, to a given R, and their magnetic moments. Previous results on the matter are also discussed.

Nonquasiparticle states in Co2MnSi evidenced through magnetic tunnel junction spectroscopy measurements.

We investigate the effects of electronic correlations in the full-Heusler Co2MnSi, by combining a theoretical analysis of the spin-resolved density of states with tunneling-conductance spectroscopy measurements using Co2MnSi as electrode. Both experimental and theoretical results confirm the existence of so-called nonquasiparticle states and their crucial contribution to the finite-temperature spin polarization in this material.

Magnetic properties and electronic structures of R-Ni-B compounds where R is a heavy rare earth.

Magnetic measurements were performed in the temperature range 4.2-300 K and fields up to 70 kOe on R(3)Ni(7)B(2) compounds with R = Gd, Tb, Dy, Ho, Er. The Curie temperatures decrease from 38.5 K (Gd) to 7 K (Er). Band structure calculations show that nickel, at 0 K, has a very small magnetic polarization, oriented antiparallel to the rare-earth moment. The XPS measurements suggest the presence of unoccupied Ni3d states. The reciprocal susceptibilities follow a Curie-Weiss type behaviour. Effective nickel moments of 1.33 ± 0.25 µ(B) were determined. The magnetic behaviour of nickel is analysed in models which take into account electron correlation effects in d bands.

Half-metallic ferromagnetism induced by dynamic electron correlations in VAs.

The electronic structure of the VAs compound in the zinc-blende structure is investigated using a combined density-functional and dynamical mean-field theory approach. Contrary to predictions of a ferromagnetic semiconducting ground state obtained by density-functional calculations, dynamical correlations induce a closing of the gap and produce a half-metallic ferromagnetic state. These results emphasize the importance of dynamic correlations in materials suitable for spintronics.

Electron correlations and the minority-spin band gap in half-metallic Heusler alloys.

Electron-electron correlations affect the band gap of half-metallic ferromagnets by introducing nonquasiparticle states just above the Fermi level. In contrast with the spin-orbit coupling, a large asymmetric nonquasiparticle spectral weight is present in the minority-spin channel, leading to a peculiar finite-temperature spin depolarization effects. Using recently developed first-principle dynamical mean-field theory, we investigate these effects for the half-metallic ferrimagnetic Heusler compound FeMnSb. We discuss depolarization effects in terms of strength of local Coulomb interaction U and temperature in FeMnSb. We propose Ni(1-x)Fe(x)MnSb alloys as a perspective materials to be used in spin-valve structures and for experimental search of nonquasiparticle states in half-metallic materials.

Experimental observation and theoretical description of the pure Fano effect in the valence-band photoemission of ferromagnets.

The pure Fano effect in angle-integrated valence-band photoemission of ferromagnets has been observed for the first time. A contribution of the intrinsic spin polarization to the spin polarization of the photoelectrons 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 photocurrent 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. 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.