Spectrally-resolved femtosecond reflectivity relaxation dynamics in   undoped SDW 122-structure iron based pnictides
  We systematically investigate temperature- and spectrally-dependent optical reflectivity dynamics in AAs$_{2}$Fe$_{2}$, (A=Ba, Sr and Eu), iron-based superconductors parent spin-density-wave (SDW) compounds. Two different relaxation processes are identified. The behavior of the slower process, which is strongly sensitive to the magneto-structural transition, is analyzed in the framework of the relaxation-bottleneck model involving magnons. The results are compared to recent time resolved angular photoemission results (TR-ARPES) and possible alternative assignment of the slower relaxation to the magneto-structural order parameter relaxation is discussed. 
A. Pogrebna (1), N.Vuji\v{c}i\'c (1,2), T. Mertelj (1), G. Cao (3), Z.   A. Xu (3), J.-H. Chu (4), I. R. Fisher (4) and D. M...
cond-mat.supr-con