Normal state transport properties in single crystals of Ba1−xKxFe2As2 andNdFeAsO1−xFx

Hall effect and magnetoresistance Δρ/ρ(0) (MR) in the normal state have been measured on single crystals of Ba1−xKxFe2As2 and NdFeAsO1−xFx. Detailed analysis reveal the following conclusions: (1) For the parent phases of Ba1−xKx Fe2As2 and NdFeAsO1−xFx, large Hall effect and MR with strong temperature dependence were observed below a characteristic temperature corresponding to the antiferromagnetic/ structural transition. The field dependence of the Hall resistivity ρxy exhibits a non-linear behavior, which is accompanied by the violation of the B-square feature of the longitudinal magnetoresistivity Δρxx(B)/ρxx(0). A closer inspection further indicates that they are well related to each other and could be attributed to the multi-band effect or spin-related scattering. (2) The superconducting samples show much smaller Hall coefficient and MR in the normal state. The Hall coefficient shows a weaker temperature dependence compared to the parent phase, while the mean scattering rate 1/τH has a power-law like temperature dependence as 1/τH ∝ Tn (n = 2-3). (3) For a Ba1−xKxFe2 As2 sample with Tc = 36 K, the field dependence of MR is complicated and the feature varies in different temperature regions. A drastic change of Δρ/ρ(0) was found between 80 K and 100 K, which corresponds very well to the maximum of the temperature derivative of the resistivity. This may be attributed to the spin-related scattering of electrons. (4) A comparison between the parent phase and the superconducting sample with Tc = 50 K in NdFeAsO1−xFx suggests that the electronic transport properties in the normal state cannot be easily understood with the simple multi-band model, while a picture concerning a suppression to the quasiparticle density of states at the Fermi energy is more reasonable.