Crossover in the magnetic response of single-crystalline Ba$_{1-x}$K$_x$Fe$_2$As$_2$ and Lifshitz critical point evidenced by Hall effect measurements

TL;DR

This study investigates how magnetic and electronic properties in Ba$_{1-x}$K$_x$Fe$_2$As$_2$ evolve with doping, revealing a Lifshitz transition and an incoherence-coherence crossover through Hall effect and susceptibility measurements.

Contribution

It provides detailed doping-dependent Hall and susceptibility data, identifying a Lifshitz critical point and associated electronic crossover in Ba$_{1-x}$K$_x$Fe$_2$As$_2$.

Findings

Magnetic susceptibility crosses over from linear-T to KFe$_2$As$_2$-type response with doping.

Hall coefficient behavior changes markedly around the Lifshitz transition at x=0.80.

Characteristic temperature T* suggests an incoherence-coherence crossover.

Abstract

We report the doping evolution of magnetic susceptibility $\chi (T)$ and Hall coefficient $R_H$ in high quality Ba$_{1-x}$K$_x$Fe$_2$As$_2$ ($0.13 \leq x \leq 1$) single crystals. It is found that the normal-state magnetic susceptibility of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ compounds undergoes a crossover from linear-$T$ dependence in the undoped and underdoped samples into KFe$_2$As$_2$-type magnetic response in the overdoped samples with increasing K content. Hall coefficient $R_H$ of underdoped sample $x$=0.22 shows a rapid increase above spin-density-wave transition temperature $T_{SDW}$. Below $T_{SDW}$, it increases slowly. $R_H$ of optimally doped and slightly overdoped samples ($0.34 \leq x \leq 0.65$) shows relative weak temperature dependence and saturation tendency below 150 K. However, $R_H$ of K heavily overdoped samples ($0.80 \leq x \leq 1$) increases rapidly below 150 K. Meanwhile, Hall angle $cot \theta _H$ displays a concave temperature dependence within the doping range $0.22 \leq x \leq 0.55$, whereas it changes to a convex temperature dependence within the doping range $0.65 \leq x \leq 1$. The dramatic change coincides with Lifshitz transition occurred around the critical doping $x$=0.80, where ARPES measurements had confirmed that electron pocket disappears with excess hole doping in Ba$_{1-x}$K$_x$Fe$_2$As$_2$ system. It is suggested that the characteristic temperature $T$* at around $120 \sim 150$ K observed in susceptibility and Hall coefficient, as well as previously reported resistivity data, may indicate an incoherence-coherence crossover in Ba$_{1-x}$K$_x$Fe$_2$As$_2$ system.