title: Unconventional superconductivity of NdFeAsO(0.82)F(0.18) indicated by the low temperature dependence of the lower critical field H(c1).
abstract: We measured the initial M-H curves for a sample of the newly discovered superconductor NdFeAsO(0.82)Fe(0.18), which had a critical temperature, T(c), of 51 K and was fabricated at the high pressure of 6 GPa. The lower critical field, H(c1), was extracted from the deviation point of the Meissner linearity in the M-H curves, which show linear temperature dependence in the low temperature region down to 5 K. The H(c1)(T) indicates no s-wave superconductivity, but rather an unconventional superconductivity with a nodal gap structure. Furthermore, the linearity of H(c1) at low temperature does not hold at high temperature, but shows other characteristics, indicating that this superconductor might have multi-gap features. Based on the low temperature nodal gap structure, we estimate that the maximum gap magnitude Δ(0) = (1.6 ± 0.2)  k(B)T(c).
authors.affiliation: Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, New South Wales 2522, Australia.
authors.forename: X L
authors.initials: XL
authors.lastname: Wang
authors.forename: S X
authors.initials: SX
authors.lastname: Dou
authors.forename: Zhi-An
authors.initials: ZA
authors.lastname: Ren
authors.forename: Wei
authors.initials: W
authors.lastname: Yi
authors.forename: Zheng-Cai
authors.initials: ZC
authors.lastname: Li
authors.forename: Zhong-Xian
authors.initials: ZX
authors.lastname: Zhao
authors.forename: Sung-Ik
authors.initials: SI
authors.lastname: Lee