We show magnetotransport results on Ba(Fe1 − xCox )2As2 (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. 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 < 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. We show that FLSC, which might have the same origin as the bulk SC, coexists with AFM as a result of competing SC and AFM orders. The temperature Tfl where FLSC sets in is close to the optimal bulk transition temperature T c , suggesting that FLSC is a precursor state to bulk SC. Since the suppression of T f l is in the vicinity of the onset of bulk superconductivity (x ≈ 0.03), in the doping range where a maximum in the orbital order emerges, we speculate that besides spin ﬂuctuations, orbital ﬂuctuations may also play an important role in the emergence of unconventional See the publication for details. SC in iron-based superconductors.
Filamentary superconductivity across the phase diagram of Ba(Fe,Co)2As2 [Phys. Rev. B 86, 064521 (2012)]