F. Kurth

Strong Tc dependence for strained epitaxial Ba(Fe1−xCox)2As2 thin films

Ba(Fe1−xCox)2As2 superconducting thin films have been grown on SrTiO3, (La,Sr)(Al,Ta)O3, LaAlO3, and YAlO3 (YAO) single crystal substrates by pulsed laser deposition. All the films, except on YAO, have been grown epitaxially without buffer layers. The films deposited on YAO contained 45° in-plane rotated grains and showed a broad superconducting transition. The onset Tc of the films is observed to increase from 16.2 to 24.5 K with increasing c/a, mainly due to a slight distortion of the AsFe4 tetrahedron. From this correlation, we expect that higher superconducting transition temperatures than 24.5 K in a strained epitaxial film may be possible.

Scaling behavior of the critical current in clean epitaxial Ba(Fe1-xCox)2As2 thin films

The angular-dependent critical current density, Jc(theta), and the upper critical field, Hc2(theta), of epitaxial Ba(Fe1-xCox)2As2 thin films have been investigated. No Jc(theta) peaks for H || c were observed regardless of temperatures and magnetic fields. In contrast, Jc(theta) showed a broad maximum at theta=90 degree, which arises from intrinsic pinning. All data except at theta=90 degree can be scaled by the Blatter plot. Hc2(theta) near Tc follows the anisotropic Ginzburg-Landau expression. The mass anisotropy increased from 1.5 to 2 with increasing temperature, which is an evidence for multi-band superconductivity.

Coherent interfacial bonding on the FeAs tetrahedron in Fe/Ba(Fe1-xCox)2As2 bilayers

We demonstrate the growth of epitaxial Fe/Ba(Fe1−xCox)2As2 bilayers on MgO(001) and (La,Sr)(Al,Ta)O3(001) single crystal substrates using pulsed laser deposition (PLD). This architecture produces a coherent interfacial bond between body-centered cubic iron and Ba(Fe1−xCox)2As2 (Ba–122). The superconducting transition temperatures for both bilayers remain close to that of the PLD target. Direct observation of interfacial bonding between Fe and the Ba–122 FeAs sublattice by atomic resolution transmission electron microscopy implies that this bilayer architecture may work for other iron pnictide systems and pave the way for their fabrication into superconducting/ferromagnetic heterostructures.

Epitaxial Growth of Superconducting Ba(Fe1-xCox)2As2 Thin Films on Technical Ion Beam Assisted Deposition MgO Substrates

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 105 Acm-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.

Influence of Fe buffer thickness on the crystalline quality and the transport properties of Fe/Ba(Fe1−xCox)2As2 bilayers

The implementation of an Fe buffer layer is a promising way to obtain epitaxial growth of Co-doped BaFe2As2 (Ba-122). However, the crystalline quality and the superconducting properties of Co-doped Ba-122 are influenced by the Fe buffer layer thickness, dFe. The well-textured growth of the Fe/Ba-122 bilayer with dFe = 15 nm results in a high Jc of 0.45 MAcm

BaFe1.8Co0.2As2 thin film hybrid Josephson junctions

^{-2}

Versatile fluoride substrates for Fe-based superconducting thin films

at 12 K in self-field, whereas a low Jc value of 61000 Acm

Direct observation of the superconducting energy gap in the optical conductivity of the iron pnictide superconductor Ba(Fe0.9Co0.1)2As2

^{-2}

Oxypnictide SmFeAs(O,F) superconductor: a candidate for high–field magnet applications

is recorded for the bilayer with dFe = 4 nm at the corresponding reduced temperature due to the presence of grain boundaries.

Strain induced superconductivity in the parent compound BaFe2As2

Josephson junctions with iron pnictides open the way for fundamental experiments on superconductivity in these materials and their application in superconducting devices. Here, we present hybrid Josephson junctions with a BaFe1.8Co0.2As2 thin film electrode, an Au barrier, and a PbIn counter electrode. The junction shows resistively shunted junction-like current-voltage characteristics up to the critical temperature of the counter electrode of about 7.2 K. The temperature dependence of the critical current shows nearly linear behavior near TC. Well-pronounced Shapiro steps are observed at microwave frequencies of 10–18 GHz. Assuming an excess current of 200 μA at 4.2 K the effective ICRN product calculates to 7.9 μV.