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arXiv · 2109.06460

Ultrafast Optical Spectroscopy Evidence of Pseudogap and Electron-Phonon Coupling in an Iron-Based Superconductor KCa$_2$Fe$_4$As$_4$F$_2$

Chen Zhang·Qi-Yi Wu·Wen-Shan Hong·Hao Liu·Shuang-Xing Zhu·Jiao-Jiao Song·Yin-Zou Zhao·Fan-Ying Wu·Zi-Teng Liu·Shu-Yu Liu·Ya-Hua Yuan·Han Huang·Jun He·Shiliang Li·H. Y. Liu·Yu-Xia Duan·Hui-Qian Luo·Jian-Qiao Meng
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Abstract

We use ultrafast optical spectroscopy to study the nonequilibrium quasiparticle relaxation dynamics of the iron-based superconductor KCa$_2$Fe$_4$As$_4$F$_2$ with $T_c=33.5$ K. Our results reveal a possible pseudogap ($\Delta_{PG}$ = 2.4 $\pm$ 0.1 meV) below $T^*\approx 50$ K but prior to the opening of a superconducting gap ($\Delta_{SC}$(0) $\approx$ 4.3 $\pm$ 0.1 meV). Measurements under high pump fluence real two distinct, coherent phonon oscillations with 1.95 and 5.51 THz frequencies, respectively. The high-frequency $A_{1g}$(2) mode corresponds to the $c-$axis polarized vibrations of FeAs planes with a nominal electron-phonon coupling constant $\lambda_{A_{1g}(2)}$ = 0.194 $\pm$ 0.02. Our findings suggest that the pseudogap is likely a precursor of superconductivity, and the electron-phonon coupling may play an essential role in the superconducting pairing in KCa$_2$Fe$_4$As$_4$F$_2$.

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Chen Zhang, Qi-Yi Wu, Wen-Shan Hong, Hao Liu, Shuang-Xing Zhu, Jiao-Jiao Song, Yin-Zou Zhao, Fan-Ying Wu, Zi-Teng Liu, Shu-Yu Liu, Ya-Hua Yuan, Han Huang, Jun He, Shiliang Li, H. Y. Liu, Yu-Xia Duan, Hui-Qian Luo, Jian-Qiao Meng. 2021-09-14. Ultrafast Optical Spectroscopy Evidence of Pseudogap and Electron-Phonon Coupling in an Iron-Based Superconductor KCa$_2$Fe$_4$As$_4$F$_2$. https://doi.org/10.1007/s11433-021-1830-9

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