Abstract
Ultrafast quasiparticle dynamics of single. crystalline LaOFeAs were investigated by pump-probe measurement. The compound experiences structural and spin-density-wave (SDW) phase transitions at 150 K (T-S1) and 130 K (T-S2), respectively. The relaxation time of quasiparticles was somewhat temperature independent at high temperature but exhibited a sharp upturn at T-S1 and reached the maximum at approximately T-S2. The remarkable slowing down of quasiparticle relaxation time is caused by the formation of energy gap. By employing the Rothwarf-Taylor model analysis, we found that there should be already energy gaps opening just below the structural transition. The magnitude of SDW gap was identified to be 72 meV.
Published Version
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