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).
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)。
