Study of Photoinduced Phase Transition in an Organic Radical Crystal with Strong Correlated Electronic System

强相关电子体系有机自由基晶体光致相变研究

基本信息

批准号：
15340094
负责人：
TAKEDA Jun
金额：
$ 10.18万
依托单位：
National University Corporation Yokohama National University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

Since a large first order magnetic phase transition with a wide thermal hysteresis loop over wide temperature range was found in 1,3,5-trithia-2,4,6-triazapentalenyl(TTTA) crystal, an organic radical crystal is expected to be a new type of strong correlated materials suitable for studying photoinduced phase transition(PIPT) phenomena. In this research, we first experimentally and theoretically investigated the PIPT phenomena as well as electronic and magnetic structures of TTTA.We found that the photoexcitations of the charge-transfer and intramolecular π-πtransition bands (i.e.one-photon excitations) induce a low-temperature(LT) diamagnetic to high-temperature(HT) paramagnetic phase transition with a clear threshold excitation density. This nonlinear behavior shows that the photoexcitations create the HT phase clusters as precursors, and subsequently, if the total size of the clusters is beyond a critical value, the macroscopic HT order is formed in the LT phase crystal. We also found that two-photon excitation optically induces the diamagnetic to paramagnetic phase transition with large nonlinear response.We investigated theoretically the crystal structures as well as electronic structures by means of the ab-initio molecular dynamics method based on the local density approximation. We found that the LT phase is a Peierls insulator while the HT phase is a Mott insulator.We also developed a femtosecond real-time pump-probe imaging spectroscopy applicable to irreversible photoreactions such as the PIPT in solids, which allows real-time mapping of frequency-and time-resolved transient absorbance in a wide spectral and temporal region at once.

由于在1,3,5-3,4,6-4,6-三唑烷基苯基（TTTA）晶体中发现有机自由基晶体有望是一种新型的强相关材料，因此在1,3,5-3,4,6-三酶苯基（TTTTA）晶体中发现了在宽温度范围内具有广泛的热滞后环的大磁相变。 In this research, we first experimentally and theoretically investigated the PIPT phenomena as well as electronic and magnetic structures of TTTA.We found that the photoexcitations of the charge-transfer and intramolecular π-πtransition bands (i.e.one-photon excitements) induce a low-temperature(LT) diamagnetic to high-temperature(HT) paramagnetic phase transition with a clear阈值兴奋密度。这种非线性行为表明，光激发创建HT相簇作为前体，随后，如果簇的总大小超出了临界值，则在LT相晶体中形成宏观HT顺序。 We also found that two-photon exciting optically induces the diamagnetic to paramagnetic phase transition with large nonlinear response.We investigated theoretical the crystal structures as well as electronic structures by means of the ab-initio molecular dynamics method based on the local density approximation.We found that the LT phase is a Peierls insulator while the HT phase is a Mott insulator.We also developed a femtosecond real-time适用于不可逆的光电反应的泵探针成像光谱，例如固体中的PIPT，它允许在广泛的光谱和临时区域中实时映射频率和时间分辨的瞬时吸收。