Fermi surface reconstruction in (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ (0.44 $\leq x \leq$ 1) probed by thermoelectric power measurements

TL;DR

This study uses thermoelectric power measurements to identify Fermi surface reconstructions in (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$, revealing Lifshitz transitions at specific doping levels related to changes in electronic topology.

Contribution

It provides experimental evidence of Fermi surface reconstructions in (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ through thermoelectric power, correlating with ARPES findings and identifying Lifshitz transitions.

Findings

Minimum in thermoelectric power at x~0.55 indicating a Lifshitz transition.

Change in thermoelectric power plateau at x~0.8-0.9.

Fermi surface topology change related to hole pocket transformation.

Abstract

We report in-plane thermoelectric power measurements on single crystals of (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ (0.44 $\leq x \leq$ 1). We observe a minimum in the S$|_{T=const}$ versus x at x ~ 0.55 that can be associated with the change in the topology of the Fermi surface, a Lifshitz transition, related to the electron pockets at the center of M point crossing the Fermi level. This feature is clearly observable below ~ 75 K. Thermoelectric power also shows a change in the x ~ 0.8 - 0.9 range, where maximum in the thermoelectric power collapses into a plateau. This Lifshitz transition is most likely related to the reconstruction of the Fermi surface associated with the transformation of the hole pockets at the M point into four blades as observed by ARPES measurements.