Ultrafast optical spectroscopy evidence of pseudogap and electronphonon coupling in an iron-based superconductor KCa_(2)Fe_(4)As_(4)F_(2)  

作　　者：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 Hai-Yun Liu Yu-Xia Duan Hui-Qian Luo Jian-Qiao Meng 

机构地区：[1]School of Physics and Electronics,Central South University,Changsha 410083,China [2]Beijing National Laboratory for Condensed Matter Physics,Institute of Physics,Chinese Academy of Sciences,Beijing 100190,China [3]School of Physical Sciences,University of Chinese Academy of Sciences,Beijing 100049,China [4]Songshan Lake Materials Laboratory,Dongguan 523808,China [5]Beijing Academy of Quantum Information Sciences,Beijing 100193,China

出　　处：《Science China(Physics,Mechanics & Astronomy)》2022年第3期92-98,共7页中国科学：物理学、力学、天文学（英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.51502351,12074436,U2032204,11822411,11961160699,and 11874401);the National Key Research and Development Program of China(Grant Nos.2018YFA0704200,2017YFA0303100;2017YFA0302900);the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(CAS)(Grant Nos.XDB25000000;XDB07020300);the K.C.Wong Education Foundation(Grant No.GJTD-2020-01);support from the Innovation-driven Plan in Central South University(Grant No.2016CXS032);the support from the Youth Innovation Promotion Association of CAS(Grant No.Y202001);the Beijing Natural Science Foundation(Grant No.JQ19002)。

摘　　要：We use ultrafast optical spectroscopy to study the nonequilibrium quasiparticle relaxation dynamics of the iron-based superconductor KCa_(2)Fe_(4)A_(s4)F_(2)with T_(c)= 33.5 K. Our results reveal a possible pseudogap(△_(PG)=(2.4 ± 0.1) me V) below T*≈ 50 K but prior to the opening of a superconducting gap(△SC(0) ≈(4.3 ± 0.1) me V). Measurements under high pump fluence reveal two distinct, coherent phonon oscillations with 1.95 and 5.51 THz frequencies, respectively. The high-frequency A1 g(2) mode corresponds to the c-axis polarized vibrations of Fe As planes with a nominal electron-phonon coupling constant λA1 g(2)= 0.194 ± 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)A_(s4)F_(2).

关 键 词：KCa_(2)Fe_(4)A_(s4)F_(2) ultrafast spectroscopy electron-phonon coupling SUPERCONDUCTIVITY 

分 类 号：O469[理学—凝聚态物理]