Observation of pseudogap-like feature above Tc in LiFeAs and (Ba0.6K0.4)Fe2As2 by ultrafast optical measurement

We utilize ultrafast optical measurement to study the quasiparticle relaxation in stoichiometric LiFeAs and nearly optimally doped (BaK)Fe2As2 crystals. According to our temperature-dependent studies of LiFeAs, we have observed pseudogap-like feature at onset temperature of ~ 55 K, which is above Tc = 15 K. In addition, the onset temperature of pseudogap ~90K was also observed in Ba0.6K0.4Fe2As2 (Tc = 36 K). Our findings seem implying that the pseudogap feature, which is due to antiferromagnetic fluctuations, is universal for the largely studied 11, 111, 122, and 1111 iron-based superconductors.