Anisotropic Electronic Mobilities in the Nematic State of the Parent Phase NaFeAs

Hall effect and magnetoresistance have been measured on single crystals of the parent phase NaFeAs under a uniaxial pressure. Although significant difference of the in-plane resistivity $\rho_{xx}(I\parallel a)$ and $\rho_{xx}(I\parallel b)$ with the uniaxial pressure along $b$-axis was observed, the transverse resistivity $\rho_{xy}$ shows a surprisingly isotropic behavior. Detailed analysis reveals that the Hall coefficient $R_\mathrm{H}$ measured in the two orthogonal configurations ($I\parallel a$-axis and $I\parallel b$-axis) coincide very well and exhibit a deviation from the high temperature background at around the structural transition temperature $T_{\mathrm{s}}$. Furthermore, the magnitude of $R_\mathrm{H}$ increases remarkably below the structural transition temperature. This enhanced Hall coefficient is accompanied by the non-linear transverse resistivity versus magnetic field and enhanced magnetoresistance, which can be explained very well by the two band model with anisotropic mobilities of each band. Our results together with the two band model analysis clearly show that the anisotropic in-plane resistivity in the nematic state is closely related to the distinct quasiparticle mobilities when they are moving parallel or perpendicular to the direction of the uniaxial pressure.