JST TRIP

Ibaraki, Japan
Ibaraki, Japan
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Mele P.,Kyushu Institute of Technology | Matsumoto K.,Kyushu Institute of Technology | Haruyama Y.,Kyushu Institute of Technology | Mukaida M.,JST TRIP | And 9 more authors.
Superconductor Science and Technology | Year: 2010

Epitaxial Fe-Te-S thin films (thickness range 100-200nm) were deposited by pulsed laser deposition at 400 °C on SrTiO3(100) and MgO(100) single-crystal substrates. The films reached the zero-resistance condition: Tc 0 = 3.54K for on SrTiO3 and 5.37K for on MgO, and presented a large upper critical field: T for on SrTiO3 and 74.2T for on MgO, using 90% of the normal state resistance and the Werthamer-Helfand-Hohenberg model. The coherence length ξ0 is very short: 2.30nm for on SrTiO3 and 2.10nm for on MgO. The film grown on MgO showed T; then the isotropic parameter γ is 1.09. The best J c observed is 104Acm-2 (at 2K, self-field) for the sample deposited on MgO. © 2010 IOP Publishing Ltd.


Maiorov B.,Los Alamos National Laboratory | Mele P.,Hiroshima University | Baily S.A.,Los Alamos National Laboratory | Weigand M.,Los Alamos National Laboratory | And 13 more authors.
Superconductor Science and Technology | Year: 2014

We present the complete superconducting upper critical field (H c2) - temperature (T) diagram of FeTeS films measured at three crystalline orientations (H ∥ c, 45° and ab). We find that Hc2 is almost isotropic in magnetic field orientation with μ0Hc2 (T = 0) ∼ 30 T and a transition temperature of Tc ∼ 7 K. A small but clear Hc2 angular anisotropy is observed, with a crossover around T = 0.7Tc, from Hc2 (∥ c) < Hc2 (∥ ab) for T > 0.7Tc to H c2 (∥ c) > Hc2 (∥ ab) for T < 0.7T c. This change in the anisotropy is similar to that observed in FeTeS and FeTeSe single crystals but occurs at a higher T/Tc for our film. We analyze the Hc2 (T) in terms of pair-breaking mechanisms and two-band superconductor theory. Understanding the inversion of Hc2 opens the possibility to adjust the effective anisotropy of superconductors for different applications. © 2014 IOP Publishing Ltd.


Mele P.,Hiroshima University | Matsumoto K.,Kyushu Institute of Technology | Fujita K.,Kyushu Institute of Technology | Yoshida Y.,JST TRIP | And 7 more authors.
Superconductor Science and Technology | Year: 2012

Epitaxial Fe-Te-Se thin films were deposited by pulsed laser deposition at 250-600°C on SrTiO 3 (100), MgO (100), LaAlO 3 (100) and CaF 2 (100) single crystal substrates. The best superconducting film was grown on CaF 2: K and K with T dep=300°C and 3Hz. Critical current density J c (T=4.2K) was 0.41×10 6Acm 2 at 0T and 0.23×10 6Acm 2 at 9T. The angular dependence of J c shows a broad c-axis correlated peak when B3T. © 2012 IOP Publishing Ltd.


Shamoto S.,Japan Atomic Energy Agency | Ishikado M.,Japan Atomic Energy Agency | Wakimoto S.,Japan Atomic Energy Agency | Kodama K.,Japan Atomic Energy Agency | And 4 more authors.
Journal of Physics: Conference Series | Year: 2012

Low-energy spin excitations on polycrystalline LaFeAsO 1-xF x samples have been studied by inelastic neutron scattering. The Q-integrated dynamical spin susceptibility χ″(ω) at 11 meV decreases with increasing fluorine content x across the phase transition from antiferromagnetic to superconducting phases. For superconducting samples, a peak in χ″(ω) develops at ω=E res below T c, accompanied by its reduction below E res. Fe 3d orbital contribution on the dynamical spin susceptibility and the electron scattering between Γ and M Fermi surfaces are discussed.


Shamoto S.,Japan Atomic Energy Agency | Wakimoto S.,Japan Atomic Energy Agency | Kodama K.,Japan Atomic Energy Agency | Ishikado M.,Japan Atomic Energy Agency | And 18 more authors.
Physica C: Superconductivity and its Applications | Year: 2011

Low-energy spin excitations have been studied on polycrystalline LaFeAsO 1-xF x samples by inelastic neutron scattering. The Q-integrated dynamical spin susceptibility χ″(ω) of the superconducting samples is found to be comparable to that of the magnetically ordered parent sample. On the other hand, χ″(ω) almost vanishes at x = 0.158, where the superconducting transition temperature T c is suppressed to 7 K. In addition, χ″(ω) in optimally doped LaFeAsO 0.918F 0.082 with T c = 29 K exhibits a spin resonance mode. The peak energy, E res, when scaled by k BT c is similar to the value of about 4.7 reported in other high-T c iron-based superconductors. This result suggests that there is intimate relationship between the dynamical spin susceptibility and high-T c superconductivity in iron-based superconductors, and is consistent with a nesting condition between Fermi surfaces at the Γ and M points. © 2011 Elsevier B.V. All rights reserved.

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