Spin density wave dynamics in iron based pnictides
Mimoza Naseska, Department of Complex Matter, JSI
We present ultrafast optical time-resolved spectroscopy measurements of the ultrafast system trajectory through the spin density wave (SDW) phase transition in SrFe2As2 and EuFe2As2. Using the standard pump-probe technique we determined the threshold fluence for the nonthermal destruction of the SDW order (Fth ≈ 0.2 mJ/cm2) at two different pump-photon energies (1.55 eV and 3.1 eV). The SDW destruction timescale obtained from the multipulse measurements is ~ 150 fs. We found that the destruction pulse penetration depth in the mJ/cm2 excitation-fluences range significantly exceeds the equilibrium optical penetration depth suggesting the absorption saturation. The recovery dynamics of the SDW order was simulated using an extended three temperature model (3TM). The analysis suggests that the optical-phonons energy-relaxation surprisingly plays an important role in the recovery of almost exclusively electronically driven SDW order.