Myung Whun Kim

Origin of the 2 eV peak in optical absorption spectra of LaMnO3: an explanation based on the orbitally degenerate Hubbard model

We investigated the temperature-dependent optical absorption spectra of LaMnO3 and NdMnO3 epitaxial thin films. We found that both spectra have strong absorption features around 2 eV, and that the 2 eV peak of LaMnO3 has a weak temperature dependence. As the La ions are replaced with Nd ions, the spectral weight of the peak becomes suppressed. From careful comparisons with the orbitally degenerate Hubbard model, we could explain most of the spectral features of the 2 eV peak observed in the absorption spectra. We also found a fine structure of three sub-peaks in the 2 eV peak, whose origin was considered based on currently available ideas.

Magnetic-field-dependent optical studies of Pr0.69Ca0.31MnO3

Abstract We investigated magnetic-field-dependent optical conductivity spectra σ ( ω ) of Pr 0.69 Ca 0.31 MnO 3 at 4.2 K, which was in a charge-ordered insulating state at 0 T. With increasing the magnetic field up to 12 T, we observed an insulator–metal transition around 4 T and large spectral weight changes up to 4 eV. Especially, we found that the spectral weight above 0.5 eV moved to a lower energy region and that a Drude-like peak appeared clearly at 12 T. By analyzing dielectric response changes, we suggested that the field-dependent insulator–metal transition might occur through a percolation process of ferromagnetic metal domains. On the other hand, with decreasing the magnetic field from 12 to 0 T, σ ( ω ) showed little changes, which showed that the ferromagnetic metallic state did not return to the insulating state.