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

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• Phase Competition and Anomalous Thermal Evolution in High-Temperature Superconductors
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• Infrared probe of the gap evolution across the phase diagram of Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$
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• Optical and photoemission investigation of structural and magnetic transitions in the iron-based superconductor Sr${}_{0.67}$Na${}_{0.33}$Fe${}_2$As${}_2$
• Pseudogap and Strong Pairing Induced by Incipient and Shallow Bands in the Quasi-Two-Dimensional KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Possible superconducting fluctuation and pseudogap state above $T_c$ in CsFe${}_2$As${}_2$
• Signatures of superconducting and pseudogap phases in ultrafast transient reflectivity of Ca(Fe0.927Co0.073)2As2
• Unconventional superconductivity after the BCS paradigm and empirical rules for the exploration of high temperature superconductors
• The Frenkel line and the pseudogap: an analogy between classical and electronic fluids