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

We show magnetotransport results on Ba(Fe1-xCox)(2)As-2 (0.0 <= x <= 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. Asignificant 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 <= x <= 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.