Normal metal-superconductor decoupling as a source of thermal fluctuation noise in transition-edge sensors J. Appl. Phys. 112, 034515 (2012) Transport critical-current density of superconducting films with hysteretic ferromagnetic dots AIP Advances 2, 022166 (2012) Pressure effects on strained FeSe0.5Te0.5 thin films J. Appl. Phys. 111, 112610 (2012) Magnetoresistance and transistor-like behavior of a double quantum-dot via crossed Andreev reflections J. Appl. Phys. 111, 113905 (2012) What are the internal field and the vortex density along the edges of a coated conductor or a superconducting bridge carrying current?

No abstract

LaFeAsO 1-x F x thin films were deposited successfully on (001)-oriented LaAlO 3 and MgO substrates from stoichiometric LaFeAsO 1-x F x polycrystalline targets with fluorine concentrations up to x = 0.25 by PLD. Room temperature deposition and post annealing of the films yield nearly phase pure films with a pronounced c-axis texture and a strong biaxial in-plane orientation.Transport measurements show metallic resistance and onset of superconductivity at 11 K. µ 0 H c2 (T) was determined by resistive measurements and yield µ 0 H c2 values of 3 T at 3.6 K for µ 0 H || c and 6 T at 6.4 K for µ 0 H || ab.

The biaxially textured growth of superconducting Co-doped BaFe2As2 (Ba-122) thin films has been realized on ion beam assisted deposition (IBAD) MgO coated conductor templates by employing an iron buffer architecture. The iron pnictide coated conductor showed a superconducting transition temperature of 21.5 K, which is slightly lower than that of Co-doped Ba-122 films on single crystalline MgO substrates. A self-field critical current density of over 10 5 A·cm −2 has already been achieved even at 8 K. The current experiment highlights the potential of possible coated conductor applications of the iron-based superconductors.

Having succeeded in the fabrication of epitaxial superconducting LaFeAsO(1-x)F(x) thin films we performed an extensive study of electrical transport properties. In the face of multiband superconductivity we can demonstrate that an anisotropic Ginzburg-Landau scaling of the angular dependent critical current densities can be adopted, although being originally developed for single band superconductors. In contrast with single band superconductors the mass anisotropy of LaFeAsO(1-x)F(x) is temperature dependent. A very steep increase of the upper critical field and the irreversibility field can be observed at temperatures below 6 K, indicating that the band with the smaller gap is in the dirty limit. This temperature dependence can be theoretically described by two dominating bands responsible for superconductivity. A pinning force scaling provides insight into the prevalent pinning mechanism and can be specified in terms of the Kramer model.

The temperature-dependent optical reflectivity and complex transmissivity of an epitaxially grown Ba͑Fe 0.9 Co 0.1 ͒ 2 As 2 thin film were measured over a wide frequency range ͑4 -35 000 cm −1 ͒. The opening of the superconducting gap 2⌬ 0 = ͑3.7Ϯ 0.3͒ meV is directly observed by vanishing optical conductivity at 30 cm −1 for T Ͻ T c = 20 K. While in this range the measured temperature-and frequency-dependent electrodynamic properties agree well with the BCS predictions of a nodeless order parameter, unexpectedly a strong quasiparticle absorption shows up below 1.5 meV. The spectral weight of the condensate 1.94ϫ 10 7 cm −2 corresponds to a penetration depth = 3600 Å.

We have measured the complex dynamical conductivity, σ = σ1 + iσ2, of superconducting Ba(Fe0.9Co0.1)2As2 (Tc = 22 K) at terahertz frequencies and temperatures 2 -30 K. In the frequency dependence of σ1 below Tc, we observe clear signatures of the superconducting energy gap opening. The temperature dependence of σ1 demonstrates a pronounced coherence peak at frequencies below 15 cm −1 (1.8 meV). The temperature dependence of the penetration depth, calculated from σ2, shows power-law behavior at the lowest temperatures. Analysis of the conductivity data with a two-gap model, gives the smaller isotropic s-wave gap of ∆A = 3 meV, while the larger gap is highly anisotropic with possible nodes and its rms amplitude is ∆0 = 8 meV. Overall, our results are consistent with a two-band superconductor with an s± gap symmetry.

Fe-based superconductors bridge a gap between MgB2 and the cuprate high temperature superconductors as they exhibit multiband character and transition temperatures up to around 55 K. Investigating Fe-based superconductors thus promises answers to fundamental questions concerning the Cooper pairing mechanism, competition between magnetic and superconducting phases, and a wide variety of electronic correlation effects. The question addressed in this review is, however, is this new class of superconductors also a promising candidate for technical applications? Superconducting film-based technologies range from high-current and high-field applications for energy production and storage to sensor development for communication and security issues and have to meet relevant needs of today’s society and that of the future. In this review we will highlight and discuss selected key issues for Fe-based superconducting thin film applications. We initially focus our discussion on the understanding of physical properties and actual problems in film fabrication based on a comparison of different observations made in the last few years. Subsequently we address the potential for technological applications according to the current situation.