Femtosecond Photo-Induced Phenomena in Multiferroic Hexagonal Manganite YMnO3

Abstract

Transient optical anisotropy in the hexagonal manganite YMnO3excited by linearly and circularly polarized laser pulses has been observed. The photo-induced anisotropy was investigated by the pump-probe technique based on a femtosecond Ti:sapphire laser generating optical pulses at the photon energy of 1.55 eV. Temporal and spectral dependencies of the photo-induced optical rotation and ellipticity were analyzed by a theoretical model considering ultrafast population and relaxation processes near the interband transitions from the hybridized O2−(2p)-Mn3+(3d) (Γ1) to the Mn3+(3d3z2−r2) (Γ5) states at photon energies of the laser excitation. Very short relaxation time of ~10 fs, which is the Raman coherence time between the excited Γ5|x> and Γ5|y> states, has been determined. It is found that this coherence time is much shorter than a charge relaxation time of ~500 fs between the Γ5|x,y> and Γ1|g> states for the interband electronic transition Γ1→Γ5.