High superconducting anisotropy and weak vortex pinning in Co doped LaFeAsO

G. Li; G. Grissonnanche; J. -Q. Yan; R. W. McCallum; T. A. Lograsso; H. D. Zhou; L. Balicas

doi:10.1103/PhysRevB.86.054517

paper

High superconducting anisotropy and weak vortex pinning in Co doped LaFeAsO

arXiv:1208.3435 · doi:10.1103/PhysRevB.86.054517

Abstract

Here, we present an electrical transport study in single crystals of LaFe $_{0.92}$ Co $_{0.08}$ AsO ( $T_{c} ≃ 9.1$ K) under high magnetic fields. In contrast to most of the previously reported Fe based superconductors, and despite its relatively low $T_{c}$ , LaFe $_{1 - x}$ Co $_{x}$ AsO shows a superconducting anisotropy which is comparable to those seen for instance in the cuprates or $γ_{H} = H_{c 2}^{ab} / H_{c 2}^{c} = m_{c} / m_{ab} ≃ 9$ , where $m_{c} / m_{ab}$ is the effective mass anisotropy. Although, in the present case and as in all Fe based superconductors, $γ \to 1$ as $T \to 0$ . Under the application of an external field, we also observe a remarkable broadening of the superconducting transition particularly for fields applied along the inter-planar direction. Both observations indicate that the low dimensionality of LaFe $_{1 - x}$ Co $_{x}$ AsO is likely to lead to a more complex vortex phase-diagram when compared to the other Fe arsenides and consequently, to a pronounced dissipation associated with the movement of vortices in a possible vortex liquid phase. When compared to, for instance, F-doped compounds pertaining to same family, we obtain rather small activation energies for the motion of vortices. This suggests that the disorder introduced by doping LaFeAsO with F is more effective in pinning the vortices than alloying it with Co.

7 figures, 7 pages, Phys. Rev. B (in press)

High superconducting anisotropy and weak vortex pinning in Co doped LaFeAsO

Abstract

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