Ultrafast Structural Dynamics along the β − γ Phase Transition Path in MnAs

  • Vidal Franck
  • Zheng Yunlin
  • Lounis Lounès
  • Coelho Leticia
  • Laulhé Claire
  • Spezzani Carlo
  • Ciavardini Alessandra
  • Popescu Horia
  • Ferrari Eugenio
  • Allaria Enrico
  • Ma Jialin
  • Wang Hailong
  • Zhao Jianhua
  • Chollet Matthieu
  • Seaberg Matthew
  • Alonso-Mori Roberto
  • Glownia James
  • Eddrief Mahmoud
  • Sacchi Maurizio


We investigate the orthorhombic distortion and the structural dynamics of epitaxial MnAs layers on GaAs(001) using static and time-resolved x-ray diffraction. Laser-induced intensity oscillations of Bragg reflections allow us to identify the optical phonon associated with orthorhombic distortion and to follow its softening along the path towards an undistorted phase of hexagonal symmetry. The frequency of this mode falls in the THz range, in agreement with recent calculations. Incomplete softening suggests that the $\beta-\gamma$ transformation deviates from a purely second-order displacive transition.