Fermi surface reconstruction in (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ (0.44   $\leq x \leq$ 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 $\leq x \leq$ 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. 
Halyna Hodovanets, Yong Liu, Anton Jesche, Sheng Ran, Eun Deok Mun,   Thomas A. Lograsso, Sergey L. Bud'ko, and Paul C. Canfield
cond-mat.supr-con