Based on experimental data on the newly synthesized iron-based superconductors and the relevant band structure calculations, we propose a minimal two-band BCS-type Hamiltonian with the interband Hubbard interaction included. We illustrate that this two-band model is able to capture the essential features of unconventional superconductivity and spin density wave (SDW) ordering in this family of materials. It is found that bound electron-hole pairs can be condensed to reveal the SDW ordering for zero and very small doping, while the superconducting ordering emerges at small finite doping, whose pairing symmetry is qualitatively analyzed to be of nodal d-wave. The derived analytical formulas not only give out a nearly symmetric phase diagram for electron and hole doping, but also is likely able to account for existing main experimental results. Moreover, we also derive two important relations for a general two-band model and elaborate how to apply them to determine the band width ratio and the effective interband coupling strength from experimental data.PACS numbers: 74.20. Rp, 75.30.Fv, 74.25.Bt Since the recent discovery of a new iron-based layered superconductor [1], intensive efforts have been focused on the nature of superconductivity in this materials both experimentally [2,3,4,5,6,7,8,9,10,11,12] and theoretically [13,14,15,16,17,18,19,20,21]. Apart from the well-known copper oxide superconductors, this family of materials exhibit higher critical temperatures, 26K in LaO 0.9 F 0. performed angle-integrated photoemission spectroscopy measurements and their data provided certain support for the existence of SDW ordering and an indication of unconventional superconductivity. In the theoretical aspect, the nature of unconventional superconductivity and the pairing mechanism have also been explored preliminarily by several groups based on the density functional theory (DFT) and dynamic mean filed theory (DMFT) [15,16,17,18,19]. It was pointed out that the electron-phonon interaction in this system may be too weak to lead such high critical temperatures [20]. The possibility of spin triplet superconductivity was also suggested [21,22].In this paper, we propose a minimal two-band BCStype Hamiltonian with an effective interband Hubbard interaction term included to model the system. The construction of our model Hamiltonian is based on band structure calculation results and intuitive physical pictures. Taking into account the main features of fermi surface for the undoped material calculated from the DFT and to capture the essential physics of the superconductivity and magnetism in the present system, we adopt a minimal version of the Fermi surface on a primary twodimensional square lattice in the Fe-Fe plane: one hole band around Γ and one electron band around M points, both crossing the Fermi surface in the undoped case. Based on rational physical considerations, we introduce an effective interband antiferromagnetic interaction and elucidate that the effective intraband antiferromagnetic coupling could induce th...

The Mott insulator Ca 2 RuO 4 is the subject of much recent attention following reports of emergent nonequilibrium steady states driven by applied electric fields or currents. In this paper, we carry out infrared nano-imaging and optical-microscopy measurements on bulk single crystal Ca 2 RuO 4 under conditions of steady current flow to obtain insight into the current-driven insulator-tometal transition. We observe macroscopic growth of the current-induced metallic phase, with nucleation regions for metal and insulator phases determined by the polarity of the current flow. A remarkable metal-insulator-metal microstripe pattern is observed at the phase front separating metal and insulator phases. The microstripes have orientations tied uniquely to the crystallographic axes, implying a strong coupling of the electronic transition to lattice degrees of freedom. Theoretical modeling further illustrates the importance of the current density and confirms a submicron-thick surface metallic layer at the phase front of the bulk metallic phase. Our work confirms that the electrically induced metallic phase is nonfilamentary and is not driven by Joule heating, revealing remarkable new characteristics of electrically induced insulator-metal transitions occurring in functional correlated oxides.

We study the fundamental question of the lattice dynamics of a metallic ferromagnet in the regime where the static long-range magnetic order is replaced by the fluctuating local moments embedded in a metallic host. We use the ab initio density functional theory + embedded dynamical mean-field theory functional approach to address the dynamic stability of iron polymorphs and the phonon softening with an increased temperature. We show that the nonharmonic and inhomogeneous phonon softening measured in iron is a result of the melting of the long-range ferromagnetic order and is unrelated to the first-order structural transition from the bcc to the fcc phase, as is usually assumed. We predict that the bcc structure is dynamically stable at all temperatures at normal pressure and is thermodynamically unstable only between the bcc-α and the bcc-δ phases of iron.

This Letter uses density functional, dynamical mean field, and Landau-theory methods to elucidate the interplay of electronic and structural energetics in the Mott metal-insulator transition. A Landau-theory free energy is presented that incorporates the electronic energetics, the coupling of the electronic state to local distortions and the coupling of local distortions to long-wavelength strains. The theory is applied to Ca_{2}RuO_{4}. The change in lattice energy across the metal-insulator transition is comparable to the change in electronic energy. Important consequences are a strongly first order transition, a sensitive dependence of the phase boundary on pressure and that the geometrical constraints on in-plane lattice parameter associated with epitaxial growth on a substrate typically change the lattice energetics enough to eliminate the metal-insulator transition entirely.

Alginate oligosaccharides (AOS) show versatile bioactivities. Although various alginate lyases have been characterized, enzymes with special characteristics are still rare. In this study, a polysaccharide lyase family 7 (PL7) alginate lyase-encoding gene, aly08, was cloned from the marine bacterium Vibrio sp. SY01 and expressed in Escherichia coli. The purified alginate lyase Aly08, with a molecular weight of 35 kDa, showed a specific activity of 841 U/mg at its optimal pH (pH 8.35) and temperature (45 °C). Aly08 showed good pH-stability, as it remained more than 80% of its initial activity in a wide pH range (4.0–10.0). Aly08 was also a thermo-tolerant enzyme that recovered 70.8% of its initial activity following heat shock treatment for 5 min. This study also demonstrated that Aly08 is a polyG-preferred enzyme. Furthermore, Aly08 degraded alginates into disaccharides and trisaccharides in an endo-manner. Its thermo-tolerance and pH-stable properties make Aly08 a good candidate for further applications.

A type of electron pairing model with spin-orbit interactions or Zeeman coupling is solved exactly in the framework of the Richardson ansatz. Based on the exact solutions for the case with spin-orbit interactions, it is shown rigorously that the pairing symmetry is of the p + ip wave and the ground state possesses time-reversal symmetry, regardless of the strength of the pairing interaction. Intriguingly, how Majorana fermions can emerge in the system is also elaborated. Exact results are illustrated for two systems, respectively, with spin-orbit interactions and Zeeman coupling.

We present density functional plus dynamical mean field studies of cubic BaRuO3 using interaction parameters previously found to be appropriate for the related materials CaRuO3 and SrRuO3. The calculated variation in transition temperature between the Ba and Sr compounds is consistent with experiment, confirming the assignment of the compounds to the Hund's metal family of materials, and also confirming the appropriateness of the values for the interaction parameters previously estimated and the appropriateness of the single-site dynamical mean field approximation for these materials. The results provide insights into the origin of magnetism and the role of the van Hove singularity in the physics of Hund's metals.

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