Terahertz-field-induced polar charge order in electronic-type dielectrics

• Published in: Nature communications Vol. 12; no. 1; pp. 953 - 11
• Main Authors: Yamakawa, H., Miyamoto, T., Morimoto, T., Takamura, N., Liang, S., Yoshimochi, H., Terashige, T., Kida, N., Suda, M., Yamamoto, H. M., Mori, H., Miyagawa, K., Kanoda, K., Okamoto, H.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 11.02.2021; Nature Publishing Group; Nature Portfolio
• Subjects: 140/125; 639/301/119; 639/766/400/561; 639/766/400/584; Charge transfer; Comparative studies; Coupling (molecular); Dimers; Electric fields; Ferroelectricity; Humanities and Social Sciences; Low temperature; multidisciplinary; Organic chemistry; Phase transitions; Photoexcitation; Physics; Quantum physics; Quantum theory; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-021-20925-x

Ultrafast electronic-phase change in solids by light, called photoinduced phase transition, is a central issue in the field of non-equilibrium quantum physics, which has been developed very recently. In most of those phenomena, charge or spin orders in an original phase are melted by photocarrier generations, while an ordered state is usually difficult to be created from a non-ordered state by a photoexcitation. Here, we demonstrate that a strong terahertz electric-field pulse changes a Mott insulator of an organic molecular compound in κ -(ET) 2 Cu[N(CN) 2 ]Cl (ET = bis(ethylenedithio)tetrathiafulvalene), to a macroscopically polarized charge-order state; herein, electronic ferroelectricity is induced by the collective intermolecular charge transfers in each dimer. In contrast, in an isostructural compound, κ -(ET) 2 Cu 2 (CN) 3 , which shows the spin-liquid state at low temperatures, a similar polar charge order is not stabilized by the same terahertz pulse. From the comparative studies of terahertz-field-induced second-harmonic-generation and reflectivity changes in the two compounds, we suggest the possibility that a coupling of charge and spin degrees of freedom would play important roles in the stabilization of polar charge order. Photoinduced phase transition is a central issue in the field of non-equilibrium quantum physics. Here, the authors demonstrate that a terahertz electric-field pulse changes a Mott insulator of an organic molecular compound to a macroscopically polarized charge-order state.