title: Longitudinal and transverse Hall resistivities in NaFe₁-xCoxAs single crystals with x = 0.022 and 0.0205: weak pinning and anomalous electrical transport properties.
abstract: The in-plane longitudinal and Hall resistivities, ρxx and ρxy, of superconducting NaFe1-xCoxAs (NFCA) single crystals with x = 0.022 and 0.0205 in the mixed state and the normal state were measured to study the electrical transport properties in nearly optimum-doping iron-based superconductors. The resistivities under magnetic fields show thermally activated behavior and a power law magnetic field dependence of activation energy has been obtained. Due to the weak flux pinning, there is no sign reversal of Hall resistivities observed for NFCA with either x = 0.022 or 0.0205. The correlation between longitudinal and Hall resistivities shows that the scaling behavior of |ρxy| ∝ (ρxx)(β) with the exponent β ≈ 2.0 is in agreement with theoretical predictions for weak-pinning superconductors. Anisotropic upper critical fields and coherence lengths with an anisotropy ratio of γ ≈ 1.63 have been deduced. Furthermore, the normal-state transport properties show that the anomalies of the linear-T resistivity, the T(2)-dependent cotangent of the Hall angle, the linear-T-like Hall number, and the magnetoresistance, which can be scaled by the modified Kohler rule, are analogous to those observed on optimally doped high-Tc superconducting cuprates and other pnictides. The longitudinal resistivity can be understood within a widely accepted scenario of the spin density-wave quantum critical point, while the transverse resistivity requires some further explanation. It is suggested that all the transport anomalies should be simultaneously taken into account when developing theory.
authors.affiliation: Graduate Institute of Applied Physics/Department of Physics, National Taiwan University, Taipei 106, Taiwan.
authors.forename: L M
authors.initials: LM
authors.lastname: Wang
authors.forename: Chih-Yi
authors.initials: CY
authors.lastname: Wang
authors.forename: Un-Cheong
authors.initials: UC
authors.lastname: Sou
authors.forename: H C
authors.initials: HC
authors.lastname: Yang
authors.forename: L J
authors.initials: LJ
authors.lastname: Chang
authors.forename: Caleb
authors.initials: C
authors.lastname: Redding
authors.forename: Yu
authors.initials: Y
authors.lastname: Song
authors.forename: Pengcheng
authors.initials: P
authors.lastname: Dai
authors.forename: Chenglin
authors.initials: C
authors.lastname: Zhang