Terahertz-Field-Induced Changes of Electronic States Associated with a Polarization Modulation in BiFeO3

• Published in: Journal of the Physical Society of Japan 2021-03, Vol.90 (3)
• Main Authors: Sono, Naoki, Kinoshita, Yuto, Kida, Noriaki, Ito, Toshimitsu, Okamoto, Hiroshi, Miyamoto, Tatsuya
• Format: Article
• Language: English
• Subjects: Charge transfer; Electric fields; Electron states; Ferroelectric materials; Ferroelectricity; Iron; Octahedrons; Polarization modulation; Reflectance; Single crystals; Wave functions; Waveforms
• ISSN: 0031-9015; 1347-4073
• DOI: 10.7566/JPSJ.90.033703

We performed terahertz-pulse-pump second-harmonic-generation (SHG)-probe and optical-reflectivity-probe measurements on a single crystal of a displacive-type ferroelectric, BiFeO3, to achieve an ultrafast control of the optical response by a terahertz pulse. By an application of a terahertz pulse with the amplitude of about 200 kV/cm along the polarization direction, the SHG intensity was modulated completely along the electric-field waveform, suggesting that the relevant ionic motions are faster than the time resolution ∼130 fs of the measurement as well as the period of the terahertz electric field. The electric-field-induced change of the reflectivity spectrum revealed that the intensities of d–d transitions in iron ions was strongly varied, while those of the charge-transfer transitions from oxygen-2p to iron-3d bands were almost unchanged. These results demonstrate that the electric field hardly modifies the wavefunction of valence electrons, but exclusively changes the distortions of iron-oxygen octahedrons. The latter effect shows that the octahedrons' distortions play dominant roles on the ferroelectric-polarization generation in BiFeO3.