Mimoza Naseska, 19.9.2018 at 13:00, F7 Seminar room

Spin density wave dynamics in iron based pnictides 

Mimoza Naseska, Department of Complex Matter, JSI

Abstract:

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 (F_th ≈ 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.

Poster [PDF]