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We discuss some properties of the ferromagnet — superconductor proximity system. In particular, the emphasis is put on the physics of the Fulde-Ferrell-Larkin-Ovchinnikov () like state. In addition to Andreev reflections it features a number of unusual thermodynamic and transport properties, like: oscillatory behavior of the pairing amplitude, density of states and superconducting transition temperature as a function of the ferromagnet thickness. Surprisingly, under certain conditions spontaneous spin polarized current is generated in the ground state of such a system. We provide some informations regarding experimental observations of this exotic state.

A recently proposed surface atom-probe technique, exchange force microscopy, is examined on an antiferromagnetic NiO (001) surface system. It is shown that atomic force of a ferromagnetic Fe probe on the surface gives a clear spin image when the probe is located within 1 Å above the contact point. Exchange force images show antiferromagnetic pattern of the Ni sites along the [110] direction and asymmetry around the O sites. The asymmetric feature comes from the superexchange interaction between the probe and the second-layer Ni atoms via the surface O ion, being a key proof of the exchange force image on observation.

We suggest to extend the well-known method of Tedrow and Meservey to investigate spin polarization in ferromagnets. Namely, metals and superconductors partially gapped by charge-density waves (CDWs) are proposed as counter-electrodes instead of ordinary superconductors. Differential conductances for the quasiparticle tunnel currents in external magnetic fields are calculated. The results are substantially different from those for ordinary superconductors.In particular, current-voltage characteristics are nonsymmetrical even for =0.

We review a recent proposal of a first principles approach to the electronic structure of materials with strong electronic correlations. The scheme combines the GW method with dynamical mean field theory, which enables one to treat strong interaction effects. It allows for a parameter-free description of Coulomb interactions and screening, and thus avoids the conceptual problems inherent to conventional “LDA+DMFT”, such as Hubbard interaction and double counting terms. We describe the application of a simplified version of the approach to the electronic structure of nickel yielding encouraging results. Finally, open questions and further perspectives for the development of the scheme are discussed.

The origin of both the long- and the short-range magnetic oscillations in films of Cr metal is studied with photoemission (PE). The experimental data are analyzed on the basis of results of the electronic structure calculations performed within the local spin-density approximation (LSDA) — layer Korringa-Kohn-Rostoker (LKKR) approach and the density functional theory (DFT) using a screened-KKR Green’s function method. It is shown that the incommensurate spin-density wave (SDW) can be monitored and important parameters of SDW-related interactions, such as coupling strength and energy of collective magnetic excitations, can be determined from the dispersion of the renormalized electronic bands close to the Fermi energy. The used approach can be applied to a large variety of other SDW systems including magnetic multilayer structures highly relevant for technological applications. The short-range PE intensity modulations at the Fermi energy are related to the quantum-well states (QWS), which were for the first time observed in 〈100〉 directions in Cr(100) layers. Possible contributions of the QWS into the short-range and the long-range magnetic coupling between marginal layers in Fe/Cr/Fe systems were discussed.

We report electronic structure calculations within density functional theory for the hydrated superconductor NaCoO1.33HO and compare the results with the parent compound NaCoO. We find that intercalation of water into the parent compound has little effect on the Fermi surface outside of the predictable effects expansion, in particular increased two-dimensionality. This implies an intimate connection between the electronic properties of the hydrated and unhydrated phases. Additional density functional calculations are used to investigate the doping dependence of the electronic structure and magnetic properties in hexagonal NaCoO. The electronic structure is highly two dimensional, even without accounting for the structural changes associated with hydration. At the local spin density approximation level, a weak itinerant ferromagnetic state is predicted for all doping levels in the range =0.3 to =0.7, with competing but weaker itinerant antiferromagnetic solutions. Comparison with experiment implies substantial magnetic quantum fluctuations. Based on the simple Fermi surface and the ferromagnetic tendency of this material, it is speculated that a triplet superconducting state analogous to that in SrRuO may exist here.

First we show that the algebra of operators entering the Hamiltonian of the model describing the strongly correlated electron system is graded (2.1) algebra. Then after a brief discussion of its atypical representations we construct the Holstein-Primako nonlinear realization of these operators which allows to carry out the systematic semiclassical approximation, similarly to the spin-wave theory of localized magnetism. The fact that the model describes the itinerant magnetism is reflected in the presence of the spinless fermions.

For the supersymmetric (2.1) algebra the supercoherent states are proposed and the partition function of the model is represented as a path integral with the help of these states.

Recently, there has been a resurgence of intense experimental and theoretical interest on the Kondo physics of nanoscopic and mesoscopic systems due to the possibility of making experiments in extremely small samples. We have carried out exact diagonalization calculations to study the e ect of energy spacing Δ in the conduction band states, hybridization, number of electrons, and disorder on the ground-state and thermal properties of strongly-correlated electron nanoclusters. For the ordered systems, the calculations reveal for the first time that Δ tunes the interplay between the Kondo and RKKY interactions, giving rise to a “Doniach phase diagram” for the nanocluster with regions of prevailing Kondo or RKKY correlations. The interplay of Δ and disorder gives rise to a Δ versus concentration phase diagram very rich in structure. The parity of the total number of electrons alters the competition between the Kondo and RKKY correlations. The local Kondo temperatures, , and RKKY interactions depend strongly on the local environment and are overall by disorder, in contrast to the hypothesis of “Kondo disorder” single-impurity models. This interplay may be relevant to experimental realizations of small rings or quantum dots with tunable magnetic properties.

We discuss the application of the density functional theory in the local density approximation (LDA) near a ferromagnetic quantum critical point. The LDA fails to describe the critical fluctuations in this regime. This provides a fingerprint of a materials near ferromagnetic quantum critical points: overestimation of the tendency to magnetism in the local density approximation. This is in contrast to the typical, but not universal, tendency of the LDA to underestimate the tendency to magnetism in strongly Hubbard correlated materials. We propose a method for correcting the local density calculations by including critical spin fluctuations. This is based on (1) Landau expansion for the free energy, evaluated within the LDA, (2) lowest order expansion of the RPA susceptibility in LDA and (3) extraction of the amplitude of the relevant (critical) fluctuations by applying the fluctuation-dissipation theorem to the difference between a quantum-critical system and a reference system removed from the quantum critical point. We illustrate some of the aspects of this by the cases of NiAl and NiGa, which are very similar metals on opposite sides of a ferromagnetic quantum critical point. LDA calculations predict that NiGa is the more magnetic system, but we find that due to differences in the band structure, fluctuation effects are larger in NiGa, explaining the fact that experimentally it is the less magnetic of the two materials.

The point contact spectra of magnetic superconductor HoNiBC/Ag based junctions is analysed in the framework of Blonder-Tinkham-Klapwijk (BTK) theory. The anomalous behavior in the curves above the Neel temperature ( ~ 5 K) is attempted to be explained by the partial suppression of superconducting gap parameter of the prevaling helical incommensurate structure.