Fermi surface in KFe2As2 determined via de Haas-van Alphen oscillation measurements

Abstract

We have completely determined the Fermi surface in KFe${}_2$As${}_2$ via de Haas-van Alphen (dHvA) measurements. Fundamental frequencies $\epsilon$, $\alpha$, $\zeta$, and $\beta$ are observed in KFe${}_2$As${}_2$. The first one is attributed to a hole cylinder near the X point of the Brillouin zone, while the others to hole cylinders at the $\Gamma$ point. We also observe magnetic breakdown frequencies between $\alpha$ and $\zeta$ and suggest a plausible explanation for them. The experimental frequencies show deviations from frequencies predicted by band structure calculations. Large effective masses up to 19 $m_e$ for $B\parallel c$ have been found, $m_e$ being the free electron mass. The carrier number and Sommerfeld coefficient of the specific heat are estimated to be 1.01 -- 1.03 holes per formula unit and 82 -- 94 mJmol${}^{-1}$K${}^{-2}$, respectively, which are consistent with the chemical stoichiometry and a direct measure of 93 mJmol${}^{-1}$K${}^{-2}$ [H. Fukazawa \textit{et al}., J. Phys. Soc. Jpn. \textbf{80SA}, SA118 (2011)]. The Sommerfeld coefficient is about 9 times enhanced over a band value, suggesting the importance of low-energy spin and/or orbital fluctuations, and places KFe${}_2$As${}_2$ among strongly correlated metals. We have also performed dHvA measurements on Ba${}_{0.07}$K${}_{0.93}$Fe${}_2$As${}_2$ and have observed the $\alpha$ and $\beta$ frequencies.

14 pages, 16 Figures, 3 Tables