Momentum dependent ultrafast electron dynamics in antiferromagnetic   EuFe2As2
  Employing the momentum-sensitivity of time- and angle-resolved photoemission spectroscopy we demonstrate the analysis of ultrafast single- and many-particle dynamics in antiferromagnetic EuFe2As2. Their separation is based on a temperature-dependent difference of photo-excited hole and electron relaxation times probing the single particle band and the spin density wave gap, respectively. Reformation of the magnetic order occurs at 800 fs, which is four times slower compared to electron-phonon equilibration due to a smaller spin-dependent relaxation phase space. 
L. Rettig, R. Cortes, S. Thirupathaiah, P. Gegenwart, H. S. Jeevan, M.   Wolf, J. Fink, and U. Bovensiepen
cond-mat.supr-con cond-mat.str-el