Phase separation in Jahn-Teller systems with localized and itinerant electrons

The phase diagram for doped manganites and related compounds is analyzed in terms of the Kondo-lattice model taking into account an interplay between electrons localized due to lattice distortions and those in the band states. It is shown that the number of itinerant charge carriers can be significantly lower than that implied by the doping level. The competition between the homogeneous (ferromagnetic or antiferromagnetic) and phase-separated states is discussed and a strong tendency to the phase separation was revealed for a wide doping range.     

Using Josephson vortex lattices to control terahertz radiation: tunable transparency and terahertz photonic crystals

The Josephson vortex (JV) lattice is a periodic array that scatters electromagnetic waves in the THz-frequency range. We show that JV lattices can produce a photonic band-gap structure (THz photonic crystal) with easily tunable forbidden zones controlled by the in-plane magnetic field. The scattering of electromagnetic waves by JVs results in a strong magnetic-field dependence of the reflection and transparency. Fully transparent or fully reflected frequency windows can be conveniently tuned by the in-plane magnetic field. These proposals are potentially useful for controllable THz filters.     

Magnetization of type-ii superconductors in the range of fields H c 1 ≤ H ≤ H c 2Variational Method

A variational method is proposed to find the magnetic field dependence of the magnetization of type-II superconductors in the mixed state by a self-consistent technique. This model allows for suppression of the order parameter to zero at the centers of Abrikosov vortices and also for the magnetic field dependence of the order parameter. The results can be applied to the entire range of fields H _c 1 ≤ H ≤ H _c 2 for any values of the Ginzburg-Landau parameter $\kappa > 1/\sqrt 2$ . It is shown that in weak fields where κ ? 1 the behavior of the magnetization can be described exactly in the London approximation provided that the correct value of H _c 1 is used. Near the second critical field this dependence shows good agreement with the well-known Abrikosov result. It is also shown that using the concept of isolated vortices and applying the principle of superposition of the fields and currents generated by these vortices to calculate the magnetization gives inaccurate quantitative results even in fairly weak fields. By going beyond these concepts, it was possible to allow more accurately for the influence of the vortex cores on the magnetization behavior in the intermediate range of fields H _c 1 ?H ? H _c 2 and to identify the range of validity of various approximations used widely in the literature.     

Formation of complexes of 1,4-dioxa-7,10-dithiacyclododecane-8-carbonitrile with transition and heavy metal ions

The structure of complexes of nitrile-containing macrocycle with various cations was studied using the methods of mass spectrometry, NMR spectroscopy, and X-ray structural analysis. The formation of a coordination polymer of the complex with Pb(II) was established.     

Symmetry-adapted-cluster configuration interaction study of the doublet states of HCl+: potential energy curves, dipole moments, and transition dipole moments

The electronic structure of the HCl(+) molecular ion has been calculated using the general-R symmetry-adapted-cluster configuration interaction (SAC-CI) method. The authors present the potential energy curves, dipole moments, and transition dipole moments for a series of doublet states. The data are compared with the previous CASSCF and MCSCF calculations. The SAC-CI results reproduce quite well the data available in literature and extend the knowledge on the HCl(+) electronic structure for several higher states. The calculated R-dependent behavior of both dipole moments and transition dipole moments for a series of bound and unbound states reveals an intricate dissociation process at intermediate distances (R>R(e)). The pronounced maxima in transition dipole moment (TDM) describing transitions into high electronic states (X (2)Pi-->3 (2)Pi, X (2)Pi-->3 (2)Sigma, 2 (2)Pi-->3 (2)Pi, 3 (2)Pi-->4 (2)Pi) occur at different interatomic separations. Such TDM features are promising for selection of excitation pathways and, consequently, for an optimal control of the dissociation products.     

Synthesis and catalytic properties of niobium indenyl peroxo complexes

Synthesis of four niobium sandwich peroxo complexes containing fragments of substituted indenes was performed and their structure was proved by NMR spectroscopy and ESI-MS mass spectrometry. Catalytic activity of the complexes in the oxidation of sulfides with hydrogen peroxide was studied, and a high selectivity in the oxidation of sulfides to sulfoxides and sulfones of the sandwich peroxo complexes was found.     

Magnetic patterns and flux pinning in Pd0.99Fe0.01-Nb hybrid structures

The magnetic properties of hybrid thin-film Pd_0.99Fe_0.01-Nb structures are studied by a magneto-optical technique. It is shown that, below 14 K, the samples exhibit the ferromagnetic ordering corresponding to the formation of weakly coupled ferromagnetic nanoclusters. In the clusters, the effective spin polarization of Fe ions is about 4μ_B, corresponding to that in the bulk Pd₃Fe alloy. The proximity of the ferromagnetic layer does not suppress the superconductivity in niobium. It does not affect the superconducting transition temperature but leads to an enhanced pinning and results in an increase in the critical current by about 30%. This behavior agrees well with the existence of the nanocluster structure in the ferromagnetic film.     

Adaptive control of laser modal properties

An adaptive optical system for precise control of a laser beam's mode structure has been developed. The system uses a dynamic lens based on controlled optical path deformation in a dichroic optical element that is heated with an auxiliary laser. Our method is essentially aberration free, has high dynamic range, and can be implemented with high average power laser beams where other adaptive optics methods fail. A quantitative model agrees well with our experimental data and demonstrates the potential of our method as a mode-matching and beam-shaping element for future large-scale gravitational wave detectors.     

Charge Distribution and Spin Textures in Magic-Angle Twisted Bilayer Graphene

JETP Letters - The spin density wave existing on the background of the inhomogeneous charge distribution is examined as a possible ground state of the magic-angle twisted bilayer graphene. When...     

Theory of Nematic Superconductivity in Doped Topological Insulators (Brief Review)

JETP Letters - Theoretical studies of the theory of nematic superconductivity in doped insulators of the Bi2Se3 family have been reviewed. It is experimentally shown that their transition to the...