American Physical Society, Physical review B, 17(90), 2014
DOI: 10.1103/physrevb.90.174502
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We utilize ultrafast optical spectroscopy to study the quasiparticle relaxation in stoichiometric LiFeAs crystals. According to our temperature-dependent studies, we have observed three electronic phases in LiFeAs. Below the superconducting (SC) temperature ${T}_{c}$ (=15 K), the relaxation time of quasiparticles due to the SC gaps is far longer than 50 ps in our experimental conditions. In addition to SC gaps, we have also found a gaplike feature in the SC state. This gaplike feature is evident up to 40 K, which is above the SC temperature. The quasiparticle relaxation time due to this gaplike feature is in the range of 1\char21{}2 ps. We suggest the gaplike feature in LiFeAs is induced by magnetic fluctuations.