Pseudogap in underdoped Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ as seen via optical conductivity

Abstract

We report the observation of a pseudogap in the \emph{ab}-plane optical conductivity of underdoped Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ ($x=0.2$ and 0.12) single crystals. Both samples show prominent gaps opened by a spin density wave (SDW) order and superconductivity at the transition temperatures $T_{SDW}$ and $T_c$, respectively. In addition, we observe an evident pseudogap below $T^{\ast }\sim$ 75 K, a temperature much lower than $T_{SDW}$ but much higher than $T_c$. A spectral weight analysis shows that the pseudogap is closely connected to the superconducting gap, indicating the possibility of its being a precursor of superconductivity. The doping dependence of the gaps is also supportive of such a scenario.

5 pages, 4 figures