Transport properties and asymmetric scattering in Ba$_{1-x}$K$_x$Fe$_2$As$_2$ single crystals compared to the electron doped counterparts Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$}

TL;DR

This study systematically investigates the transport properties of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ single crystals, revealing asymmetric scattering effects, doping-insensitive resistivity, and signs of quantum criticality near optimal doping.

Contribution

It provides new insights into the asymmetric scattering rates between hole and electron pockets and identifies a possible pseudogap and quantum critical behavior in hole-doped iron pnictides.

Findings

Resistivity remains unchanged with K-doping, unlike electron-doped counterparts.

Hall coefficient changes sign abruptly with slight K-doping.

Evidence of a pseudogap and quantum criticality near optimal doping.

Abstract

Resistivity, Hall effect and magnetoresistance have been investigated systematically on single crystals of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ ranging from undoped to optimally doped regions. A systematic evolution of the quasiparticle scattering has been observed. It is found that the resistivity in the normal state of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ is insensitive to the potassium doping concentration, which is very different from the electron doped counterpart Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$, where the resistivity at 300 K reduces to half value of the undoped one when the system is optimally doped. In stark contrast, the Hall coefficient R$_H$ changes suddenly from a negative value in the undoped sample to a positive one with slight K-doping, and it keeps lowering with further doping. We interpret this dichotomy due to the asymmetric scattering rate in the hole and the electron pockets with much higher mobility of the latter. The magnetoresistivity shows also a non-monotonic doping dependence indicating an anomalous feature at about 80 K to 100 K, even in the optimally doped sample, which is associated with a possible pseudogap feature. In the low temperature region, it seems that the resistivity has the similar values when superconductivity sets in disregarding the different T$_c$ values, which indicates a novel mechanism of the superconductivity. A linear feature of resistivity $\rho_{ab}$ vs. $T$ was observed just above $T_c$ for the optimally doped sample, suggesting a quantum criticality.