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

We report in-plane thermoelectric power measurements on single crystals of (Ba${}_{1-x}$K${}_x$)Fe${}_2$As${}_2$ (0.44 $\le x\le$ 1). We observe a minimum in the S${\mathrm{\mid }}_{T=const}$ 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.