Filamentary superconductivity across the phase diagram of Ba(Fe,Co)2As2

Abstract

We show magnetotransport results on Ba(Fe${}_{1\ensuremath{-}x}$Co${}_{x}$)${}_{2}$As${}_{2}$ ($0.0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.13$) single crystals. We identify the low-temperature resistance step at 23 K in the parent compound with the onset of filamentary superconductivity (FLSC), which is suppressed by an applied magnetic field in a similar manner to the suppression of bulk superconductivity (SC) in doped samples. FLSC is found to persist across the phase diagram until the long-range antiferromagnetic order is completely suppressed. A significant suppression of FLSC occurs for $0.02<x<0.04$, the doping concentration where bulk SC emerges. Based on these results and the recent report of an electronic anisotropy maximum for 0.02 $\ensuremath{\leqslant}x\ensuremath{\leqslant}$ 0.04 [Chu et al., Science 329, 824 (2010)], we speculate that, besides spin fluctuations, orbital fluctuations may also play an important role in the emergence of SC in iron-based superconductors.