Spectral dynamics of shift current in ferroelectric semiconductor SbSI

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 116; no. 6; pp. 1929 - 1933
• Main Authors: Sotome, M., Nakamura, M., Fujioka, J., Ogino, M., Kaneko, Y., Morimoto, T., Zhang, Y., Kawasaki, M., Nagaosa, N., Tokura, Y., Ogawa, N.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 05-02-2019
• Subjects: Antimony; bulk matter; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Current carriers; Electromagnetic radiation; Electron clouds; Electron transitions; Energy gap; Ferroelectric materials; Ferroelectricity; First principles; Fruits; Iodides; Optical transition; Photoelectric effect; Photoelectric emission; Photoexcitation; Photovoltaic cells; photovoltaic effect; Physical Sciences; picosecond techniques; Solar cells; Sulfur; Time; bulk matter; solar cells; picosecond techniques; ferroelectricity; photovoltaic effect
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1802427116

Photoexcitation in solids brings about transitions of electrons/holes between different electronic bands. If the solid lacks an inversion symmetry, these electronic transitions support spontaneous photocurrent due to the geometric phase of the constituting electronic bands: the Berry connection. This photocurrent, termed shift current, is expected to emerge on the timescale of primary photoexcitation process. We observe ultrafast evolution of the shift current in a prototypical ferroelectric semiconductor antimony sulfur iodide (SbSI) by detecting emitted terahertz electromagnetic waves. By sweeping the excitation photon energy across the bandgap, ultrafast electron dynamics as a source of terahertz emission abruptly changes its nature, reflecting a contribution of Berry connection on interband optical transition. The shift excitation carries a net charge flow and is followed by a swing over of the electron cloud on a subpicosecond timescale. Understanding these substantive characters of the shift current with the help of first-principles calculation will pave the way for its application to ultrafast sensors and solar cells.