With the discovery of new superconducting materials, such as the iron pnictides1, exploring their potential for applications is one of the foremost tasks. Even if the critical temperature Tc is high, intrinsic electronic properties might render applications difficult, particularly if extreme electronic anisotropy prevents effective pinning of vortices and thus severely limits the critical current density, a problem well known for cuprates2, 3, 4, 5. Although many questions concerning microscopic electronic properties of the iron pnictides have been successfully addressed5 and estimates point to a very high upper critical field6, 7, 8, 9, their application potential is less clear. Thus, we focus here on the critical currents, their anisotropy and the onset of electrical dissipation in high magnetic fields up to 65 T. Our detailed study of the transport properties of SmFeAsO0.7F0.25 single crystals reveals a promising combination of high (>2×106 A cm−2) and nearly isotropic critical current densities along all crystal directions. This favourable intragrain current transport in SmFeAs(O, F), which shows the highest Tc of 54 K at ambient pressure10, 11, 12, is a crucial requirement for possible applications. Essential in these experiments are four-probe measurements on focused-ion-beam-cut single crystals with a sub-square-micrometre cross-section, with current along and perpendicular to the crystallographic c axis.
At a glance
- Iron-based layered superconductor: La(O1−xFx)FeAs (x=0.05–0.12) with T c=26 K. J. Am. Chem. Soc. 11, 3296–3297 (2008). et al.
- Superconducting transport properties of grain boundaries in YBa2Cu3O7 bicrystals. Phys. Rev. B 41, 4038–4049 (1990). , &
- Strong to weak coupling transition in low misorientation angle thin film YBa2Cu3O7−x bicrystals. Phys. Rev. B 60, 1409–1417 (1999). , , &
- Grain boundaries in high-T c superconductors. Rev. Mod. Phys. 74, 485–549 (2002). &
- Dissipative flux-motion in high temperature superconductors. Phys. Rev. B 41, 6621–6632 (1990). , , , &
- Upper critical fields well above 100 T for the superconductor SmFeAsO0.85F0.15 with T c=46 K. Phys. Rev. B 78, 054514 (2008). et al.
- Two-band superconductivity in LaFeAsO0.89F0.11 at very high magnetic fields. Nature 453, 903–905 (2008). et al.
- Comparative high-field magnetotransport of the oxypnictide superconductors RFeAsO1−xFx (R=La, Nd) and SmFeAsO1−δ . Phys. Rev. B 78, 064511 (2008). et al.
- Effects of two gaps and paramagnetic pair-breaking effects on the upper critical field of SmFeAsO0.85 and SmFeAsO0.8F0.2 single crystals. Phys. Rev. B 80, 144512 (2009). et al.
- Anomalous transport properties and phase diagram of the FeAs-based SmFeAsO1−xFx superconductors. Phys. Rev. Lett. 101, 087001 (2008). et al.
- Superconductivity at 43 K in SmFeAsO1−xFx . Nature 453, 761–762 (2008). et al.
- Superconductivity at 55 K in iron-based F-doped layered quaternary compound Sm[O1−xFx] FeAs. Chin. Phys. Lett. 25, 2215–2216 (2008). et al.
- Single crystals of superconducting SmFeAsO1−xFy grown at high pressure. J. Phys. Condens. Matter 20, 342202 (2008). et al.
- Single crystals of LnFeAsO1−xFx (Ln=La, Pr, Nd, Sm, Gd) and Ba1−xRbxFe2As2: Growth, structure and superconducting properties. Physica C 469, 370–380 (2009). et al.
- Upper critical fields and thermally-activated transport of NdFeAsO0.7F0.3 single crystal. Phys. Rev. B 78, 174523 (2008). et al.
- The role of F-doping and oxygen vacancies on the superconductivity in SmFeAsO compounds. Supercond. Sci. Technol. 22, 025004 (2009). et al.
- Metallic in-plane and divergent out-of-plane resistivity of a high-T c cuprate in the zero-temperature limit. Phys. Rev. Lett. 77, 2065–2068 (1996). et al.
- Anisotropy of the iron pnictide superconductor Ba(Fe1−xCox)2As2 (x=0.074, T c=23 K). Phys. Rev. B 79, 094507 (2009). et al.
- Resistivity and upper critical field in KFe2As2 single crystals. J. Phys. Soc. Jpn 78, 063702 (2009). et al.
- Measurement of anisotropic resistivity and Hall constant for single-crystal YBa2Cu3O7−x . Phys. Rev. Lett. 59, 1768–1771 (1987). et al.
- Evolution of the resistivity anisotropy in Bi2Sr2−xLaxCuO6+δ single crystals for a wide range of hole doping. Phys. Rev. B 67, 104512 (2003). &
- Resistive upper critical fields and irreversibility lines of optimally doped high-T c cuprates. Phys. Rev. B 60, 12475–12479 (1999). et al.
- Anisotropy of the upper critical field and critical current in single crystal MgB2 . Phys. Rev. B 66, 180502 (2002). et al.
- Magnetization of hard superconductors. Phys. Rev. Lett. 8, 250–253 (1962).
- Anisotropic critical currents in Ba2YCu3O7 analyzed using an extended Bean model. Appl. Phys. Lett. 55, 283–285 (1989). , , , &
- Vortex phase diagram of Ba(Fe0.93Co0.07)2As2 single crystals. Phys. Rev. B 78, 224506 (2008). et al.
- Superconductivity at 23 K and low anisotropy in Rb-substituted BaFe2As2 single crystals. Phys. Rev. B 79, 104521 (2009). et al.
- High-T c superconducting materials for electric power applications. Nature 414, 368–377 (2001) insight review. , , &
- Static and dynamic mechanisms of the anomalous field dependence of magnetization in Bi–Sr–Ca–Cu–O and Bi–Pb–Sr–Ca–Cu–O single crystals. Phys. Rev. B 50, 16774–16777 (1994). et al.
- Flux pinning mechanisms in type II superconductors. Phil. Mag. 30, 293–305 (1974).
- Analysis of pinning in NdBa2Cu3O7−d superconductors. Phys. Rev. B 58, 2863–2867 (1998). , , , &
- Increase of critical currents and peak effect in Mo-substituted YBa2Cu3O7 . Phys. Rev. B 73, 224518 (2006). , &
- Supplementary Information (613 KB)