We report a new strategy to induce superconductivity in iron-based oxyarsenide. Instead of F − substitution for O 2− , we employed Th 4+ doping in GdFeAsO with the consideration of "lattice match" between Gd2O2 layers and Fe2As2 ones. As a result, superconductivity with T onset c as high as 56 K was realized in a Gd0.8Th0.2FeAsO polycrystalline sample. This Tc value is among the highest ever discovered in the iron-based oxypnictides.

By substituting Fe with the 5d-transition metal Pt in BaFe2As2, we have successfully synthesized the superconductors BaFe2−xPtxAs2. The systematic evolution of the lattice constants indicates that the Fe ions were successfully replaced by Pt ions. By increasing the doping content of Pt, the antiferromagnetic order and structural transition of the parent phase is suppressed and superconduc-tivity emerges at a doping level of about x = 0.02. At a doping level of x = 0.1, we get a maximum transition temperature Tc of about 25 K. While even for this optimally doped sample, the residual resistivity ratio (RRR) is only about 1.35, indicating a strong impurity scattering effect. We thus argue that the doping to the Fe-sites naturally leads to a high level impurity scattering, although the superconductivity can still survive at about 25 K. The synchrotron powder x-ray diffraction shows that the resistivity anomaly is in good agreement with the structural transition. The super-conducting transitions at different magnetic fields were also measured at the doping level of about x = 0.1, yielding a slope of-dHc2/dT = 5.4 T/K near Tc. Finally a phase diagram was established for the Pt doped 122 system. Our results suggest that superconductivity can also be easily induced in the FeAs family by substituting the Fe with Pt, with almost the similar maximum transition temperatures as doping Ni, Co, Rh and Ir.

We use inelastic neutron scattering to study magnetic excitations of the FeAs-based superconductor BaFe1.9Ni0.1As2 above and below its superconducting transition temperature Tc = 20 K. In addition to gradually open a spin gap at the in-plane antiferromagnetic ordering wavevector (1, 0, 0), the effect of superconductivity is to form a three dimensional resonance with clear dispersion along the c-axis direction. The intensity of the resonance develops like a superconducting order parameter, and the mode occurs at distinctively different energies at (1, 0, 0) and (1, 0, 1). If the resonance energy is directly associated with the superconducting gap energy ∆, then ∆ is dependent on the wavevector transfers along the c-axis. These results suggest that one must be careful in interpreting the superconducting gap energies obtained by surface sensitive probes such as scanning tunneling microscopy and angle resolved photoemission.PACS numbers: 74.25. Ha, 78.70.Nx Understanding the interplay between spin fluctuations and superconductivity in high-transition-temperature (high-T c ) superconductors is important because spin fluctuations may mediate electron pairing for superconductivity [1,2]. In the case of high-T c copper oxides, it is now well documented that the spin fluctuation spectrum is dominated by a collective excitation known as the resonance mode centered at the antiferromagnetic (AF) ordering wavevector Q = (1/2, 1/2) [3,4,5,6,7,8]. Although the intensity of the mode behaves like an order parameter below T c , the energy of the mode is dispersionless for wavevector transfers along the c-axis and directly tracks T c [4,5,6,7,8], thus suggesting that the mode is an intrinsic property of the two-dimensional (2D) CuO 2 planes and intimately associated with superconductivity. For FeAs-based superconductors [9,10,11,12], the presence of static AF ordering in their parent compounds (with spin structure of Fig. 1a) [13,14,15,16,17,18] and the remarkable similar doping dependent phase diagram to that of the high-T c copper oxides [15] suggest that AF spin fluctuations may also play an important role in the superconductivity of these materials. Indeed, recent neutron scattering measurements on spin fluctuations of powder samples of superconducting Ba 0.6 K 0.4 Fe 2 As 2 (T c = 38 K) [19] and crystalline electric field (CEF) excitations of Ce in CeFeAsO 0.84 F 0.16 (T c = 41 K) [20] found clear evidence for resonant-like magnetic intensity gain below T c athω ∼ 14 and 18.7 meV, respectively. However, the Ce CEF measurements give no information on the Q-dependence of the scattering [20]. Although the resonant-like scattering in Ba 0.6 K 0.4 Fe 2 As 2 occurs near the AF ordering wavevector, the powder nature of the experiment impedes to distinguish whether the resonant scattering is centered at the three-dimensional (3D) AF wavevector Q = (1, 0, 1) of its parent compound [16,17,18] or simply at a 2D AF in-plane wavevector Q = (1, 0, 0) [19].In this Letter, we report the results of inelastic neutron scattering studies of s...

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Magnetic flux structure on the surface of EuFe2(As1−xPx)2 single crystals with nearly optimal phosphorus doping levels x = 0.20, and x = 0.21 is studied by low-temperature magnetic force microscopy and decoration with ferromagnetic nanoparticles. The studies are performed in a broad temperature range. It is shown that the single crystal with x = 0.21 in the temperature range between the critical temperatures TSC = 22 K and TC = 17.7 K of the superconducting and ferro-magnetic phase transitions, respectively has the vortex structure of a frozen magnetic flux, typical for type-II superconductors. The magnetic domain structure is observed in the superconducting state below TC. The nature of this structure is discussed.

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ATP degradation is one of the most important biochemical changes in the post-mortem muscle of fish and shellfish. This process has long been recognized as an accurate way to evaluate freshness of fish and shellfish product. This review updates and condenses the overall history and recent advances in understanding the role of ATP-related compounds in post-mortem fish and shellfish muscle including a discussion of key analytical methods, their use as a freshness indicator, their roles in flavor enhancement, the factors affecting their transitions, and the possible mechanisms responsible for their impact on flavor and freshness. Moreover, some challenges and future directions for research regarding ATP-related compounds in fish and shellfish flavor and freshness are presented. With increasing consumer demands for fresh products with extended shelf life, understanding the relationships between ATP-related compounds and their involvement in the freshness and umami taste is a prerequisite for assuring the high quality of fish and shellfish.