Circular Dichroism and Superdiffusive Transport at the Surface of BiTeI

Abstract : We investigate the electronic states of BiTeI after the optical pumping with circularly polarized photons. Our data show that photoexcited electrons reach an internal thermalization within 300 fs from the arrival of the pump pulse. Instead, the dichroic contrast generated by the circularly polarized light relaxes on a timescale shorter than 80 fs. This result implies that orbital and spin polarization created by the circular pump pulse rapidly decays via manybody interaction. The remnant dichroic contrast at longer delay times is due to the helicity dependence of superdiffussive transport. We ascribe it to the lack of inversion symmetry in an electronic system far from equilibrium conditions.