Spin-dependent conductivity of iron-based superconductors in a magnetic field

We report the results of a study of magnetic field features of electron transport in heterojunctions with NS boundary inside iron-based superconductors, represented by a binary phase of $\alpha$ - FeSe and oxyarsenide pnictide LaO(F)FeAs. We used the ability of self magnetic field of the transport current to partially destroy superconductivity, no matter how low the field may be, in the NS interface area, where, due to the proximity effect, the superconducting order parameter, $\Delta$, disperses from 1 to 0 within the scale of the Ginzburg-Landau coherence length. The following features of transport were found:(i) at $T<T_{c}$, magnetoresistance in systems with different superconductors has different sign;(ii) sign and magnitude of the magnetoresistance depend on the magnitude of current and temperature, and (iii) in all operating modes where the contribution from Andreev reflection is suppressed ($(T + eV) \gtrsim \Delta$),the hysteresis of the magnetoresistance is present. Based on the results of the experiment and analysis it has been concluded that there is along-range magnetic order in th eground normal state of the iron-based superconductors studied, in the presence of itinerant magnetism of conduction electrons which determines the possibility of anisotropic spin-dependent exchange interaction with the local magnetic moments of the ions.Comment: 9 pages, 7 figure

Unfolded Scalar Supermultiplet

Unfolded equations of motion for N = 1, D = 4 scalar supermultiplet are presented. We show how the superspace formulation emerges from the unfolded formulation. To analyze supersymmetric unfolded equations we extend the \sigma_-cohomology technics to the case with several operators \sigma_. The role of higher \sigma_-cohomology in the derivation of constraints is emphasized and illustrated by the example of scalar supermultiplet.Comment: 27 pages, no figures; minor corrections: clarifications added, typos correcte

Gravitational cubic interactions for a massive mixed symmetry gauge field

In a recent paper arXiv:1107.1872 cubic gravitational interactions for a massless mixed symmetry field in AdS space have been constructed. In the current paper we extend these results to the case of massive field. We work in a Fradkin-Vasiliev approach and use frame-like gauge invariant description for massive field which works in (A)dS spaces with arbitrary values of cosmological constant including flat Minkowski space. In this, massless limit in AdS space coincides with the results of arXiv:1107.1872 while we show that it is impossible to switch on gravitational interaction for massless field in dS space.Comment: 13 page

Hybridization and spin-orbit coupling effects in quasi-one-dimensional spin-1/2 magnet Ba3Cu3Sc4O12

We study electronic and magnetic properties of the quasi-one-dimensional spin-1/2 magnet Ba3Cu3Sc4O12 with a distinct orthogonal connectivity of CuO4 plaquettes. An effective low-energy model taking into account spin-orbit coupling was constructed by means of first-principles calculations. On this basis a complete microscopic magnetic model of Ba3Cu3Sc4O12, including symmetric and antisymmetric anisotropic exchange interactions, is derived. The anisotropic exchanges are obtained from a distinct first-principles numerical scheme combining, on one hand, the local density approximation taking into account spin-orbit coupling, and, on the other hand, projection procedure along with the microscopic theory by Toru Moriya. The resulting tensors of the symmetric anisotropy favor collinear magnetic order along the structural chains with the leading ferromagnetic coupling J1 = -9.88 meV. The interchain interactions J8 = 0.21 meV and J5 = 0.093 meV are antiferromagnetic. Quantum Monte Carlo simulations demonstrated that the proposed model reproduces the experimental Neel temperature, magnetization and magnetic susceptibility data. The modeling of neutron diffraction data reveals an important role of the covalent Cu-O bonding in Ba3Cu3Sc4O12.Comment: 11 pages, 12 figure

A minimal BV action for Vasiliev's four-dimensional higher spin gravity

The action principle for Vasiliev's four-dimensional higher-spin gravity proposed recently by two of the authors, is converted into a minimal BV master action using the AKSZ procedure, which amounts to replacing the classical differential forms by vectorial superfields of fixed total degree given by the sum of form degree and ghost number. The nilpotency of the BRST operator is achieved by imposing boundary conditions and choosing appropriate gauge transitions between charts leading to a globally-defined formulation based on a principal bundle.Comment: 39 pages, 1 figure. Additional comments in the conclusion

Supersymmetric Higher Spin Theories

We revisit the higher spin extensions of the anti de Sitter algebra in four dimensions that incorporate internal symmetries and admit representations that contain fermions, classified long ago by Konstein and Vasiliev. We construct the $dS_4$, Euclidean and Kleinian version of these algebras, as well as the corresponding fully nonlinear Vasiliev type higher spin theories, in which the reality conditions we impose on the master fields play a crucial role. The ${\cal N}=2$ supersymmetric higher spin theory in $dS_4$, on which we elaborate further, is included in this class of models. A subset of Konstein-Vasiliev algebras are the higher spin extensions of the $AdS_4$ superalgebras $osp(4|{\cal N})$ for ${\cal N}=1,2,4$ mod 4 and can be realized using fermionic oscillators. We tensor the higher superalgebras of the latter kind with appropriate internal symmetry groups and show that the ${\cal N}=3$ mod 4 higher spin algebras are isomorphic to those with ${\cal N}=4$ mod 4. We describe the fully nonlinear higher spin theories based on these algebras as well, and we elaborate further on the ${\cal N}=6$ supersymmetric theory, providing two equivalent descriptions one of which exhibits manifestly its relation to the ${\cal N}=8$ supersymmetric higher spin theory.Comment: 30 pages. Contribution to J. Phys. A special volume on "Higher Spin Theories and AdS/CFT" edited by M. R. Gaberdiel and M. Vasilie

Magnetically frustrated synthetic end member Mn2(PO4)OH in the triplite-triploidite family

The manganese end member of triplite-triploidite series of compounds, Mn2(PO4)OH, is synthesized by a hydrothermal method. Its crystal structure is refined in the space group P21/c with a = 12.411(1) Å, b = 13.323(1) Å, c = 10.014(1) Å, β = 108.16(1), V = 1573.3 Å3, Z = 8, and R = 0.0375. Evidenced in measurements of magnetization M and specific heat Cp, Mn2(PO4)OH reaches a long range antiferromagnetic order at TN = 4.6 K. As opposed to both triplite Mn2(PO4)F and triploidite-type Co2(PO4)F, the title compound is magnetically frustrated being characterized by the ratio of Curie-Weiss temperature Θ to Néel temperature TN of about 20. The large value of frustration strength Θ/TN stems from the twisted saw tooth chain geometry of corner sharing triangles of Mn polyhedra, which may be isolated within tubular fragments of a triploidite crystal structure. © 2017 The Royal Society of Chemistry.We thank E. V. Guseva for the X-ray spectral analysis of the sample and N. V. Zubkova for her help in the X-ray experiment. This work was supported by the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST "MISiS" project K2-2016-066 and by RFBR projects 15-05-06742, 16-02-00021 and 17-02-00211. The work was supported by Act 211 Government of the Russian Federation, contracts 02.A03.21.0004, 02.A03.21.0006 and 02.A03.21.0011

Highly mobile carriers in orthorhombic phases of iron-based superconductors FeSe1−x{}_{1-x}Sx{}_{x}

The field and temperature dependencies of the longitudinal and Hall resistivity have been measured for FeSe${}_{1-x}$S${}_{x}$ (x=0.04, 0.09 and 0.19) single crystals. The sample FeSe${}_{0.81}$S${}_{0.19}$ does not show a transition to an orthorhombic phase and exhibits at low temperatures the transport properties quite different from those of orthorhombic samples. The behavior of FeSe${}_{0.81}$S${}_{0.19}$ is well described by the simple two band model with comparable values of hole and electron mobility. In particular, at low temperatures the transverse resistance shows a linear field dependence, the magnetoresistance follow a quadratic field dependence and obeys to Kohler's rule. In contrast, Kohler's rule is strongly violated for samples having an orthorhombic low temperature structure. However, the transport properties of the orthorhombic samples can be satisfactory described by the three band model with the pair of almost equivalent to the tetragonal sample hole and electron bands, supplemented with the highly mobile electron band which has two order smaller carrier number. Therefore, the peculiarity of the low temperature transport properties of the orthorhombic Fe(SeS) samples, as probably of many other orthorhombic iron superconductors, is due to the presence of a small number of highly mobile carriers which originate from the local regions of the Fermi surface, presumably, nearby the Van Hove singularity points