Multiferroic hexagonal manganites ReMnO3studied by optics are reviewed. Their electronic structures were revealed by static linear and nonlinear spectra. Two transitions located at~1.7 eV and~2.3 eV have been observed and attributed to the interband transitions from the lower-lying Mn3+dxy/dx2-y2anddxz/dyzstates to the Mn3+d3z2-r2state, respectively. These so-called d-d transitions exhibit a blueshift as decreasing temperatures and an extra blueshift nearTN. This dramatic change indicates that the magnetic ordering seriously influences the electronic structure. On the other hand, the ultrafast optical pump-probe spectroscopy has provided the important information on spin-charge coupling and spin-lattice coupling. Because of the strongly correlation between electronic structure and magnetic ordering, the amplitude of the initial rising component inΔR/Rshows striking changes at the vicinity ofTN. Moreover, the coherent optical and acoustic phonons were observed on optical pump-probe spectroscopy. Both the amplitude and dephasing time of coherent phonons also exhibit significant changes atTN, which provide the evidence for spin-lattice interaction in these intriguing materials.
Ultrafast Optical-Pump Terahertz-Probe Spectroscopy of the Carrier Relaxation and Recombination Dynamics in Epitaxial Graphene
