Longitudinal and transverse Hall resistivities in NaFe_1−xCo_xAs single crystals withx= 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.

Weakly-correlated nodeless superconductivity in single crystals of Ca3Ir4Sn13 and Sr3Ir4Sn13 revealed by critical fields, Hall effect, and magnetoresistance measurements

“…As can be seen, the data at different temperatures show distinctly different curves, indicating that the MR orb of SIS does not obey the modified Kohler's rule. Contrary to this result of SIS, it has been demonstrated that the scaling of Kohler's rule breaks down in cases of optimum-doped YBCO, La 2−x Sr x CuO 4 , NaFe 1−x Co x As and BaFe 2 (As 1−x P x ) 2 [28,35,37] in which the MR violates the Kohler's scaling and can be scaled by the square of the Hall angle (modified Kohler's rule) in these optimally doped systems. The scenario of SDW QCP has recently been proposed to describe the normal-state transport properties [38,39].…”

“…As can be seen, the data almost fall on a straight line in the temperature range below T* and can be fitted to the equation of cotθ H = ΛT 2 + C with the parameters Λ of 1.063 (0.023) K −2 and C of 182.6 (5.7) for CIS (SIS) in an applied field of 6 T, where C corresponds to the impurity contribution. Also shown in the inset of figure 5(b) is the T 2 behavior of cotθ H for CIS and SIS at temperatures above T* with the parameters Λ and C of 32.34 (34.20) K −2 and 475.2 (946.6) for CIS (SIS) in an applied field of 3 T. The Λ value for CIS is almost two orders of magnitude larger than those observed in HTS cuprates, MgB 2 or superconducting pnictides (10 −3 ∼ 10 −2 K −2 ) [25][26][27][28]. It has been pointed out that the temperature dependence of cotθ H for many superconductors with a wide range of doping retains its simple ΛT 2 + C form at temperatures above T c even though the temperature dependence of ρ xx changes considerably [29].…”

Thermal activation energy of 3D vortex matter in NaFe1−x Co x As (x = 0.01, 0.03 and 0.07) single crystals

“…It is well known that in the mixed state, thermal fluctuations directly affect the vortex motion due to thermally activated flux flow (TAFF) in a superconductor. In the case of iron-based superconductors including "111" compounds, relatively much researches have been conducted for the understanding of the vortex dynamics through TAFF analysis [11][12][13][14][15][16]. There is a lack of systematic studies on the vortex dynamics in 111-type compounds in terms of chemical doping or applied pressure variations.…”

Magnetotransport properties and pseudogap phase diagram of superconducting EuBa2Cu3Oy thin films: the influence of Eu substitution

“…Moreover, prominent magnetic field dependences of the activation energy U appear in the experimental results. It can be observed that for most samples, U can be fitted with a power-law dependence U ∝ H −α , which has been widely followed by other type-II superconductors [32][33][34].…”