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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1,3,5-三硫-2,4,6-三氮杂五烯基（TTTA）晶体中发现了在宽温度范围内具有宽热滞回线的大一阶磁相变，有机自由基晶体有望成为一种适合研究光致相变（PIPT）现象的新型强关联材料。在这项研究中，我们首先从实验和理论上研究了 PIPT 现象以及 TTTA 的电子和磁性结构。我们发现电荷转移和分子内 π-π 过渡带的光激发（即单光子激发）会诱导低温（LT）抗磁到高温（HT）顺磁相变，并具有清晰的相变。阈值激发密度。这种非线性行为表明，光激发产生 HT 相簇作为前体，随后，如果簇的总尺寸超过临界值，则在 LT 相晶体中形成宏观 HT 有序。我们还发现双光子激发光学诱导了抗磁到顺磁的相变，具有很大的非线性响应。我们利用基于局域密度近似的从头算分子动力学方法从理论上研究了晶体结构和电子结构。我们发现LT相是Peierls绝缘体，而HT相是Mott绝缘体。我们还开发了一种飞秒实时泵浦探针成像光谱仪，适用于不可逆光反应，例如固体中的PIPT，它允许在宽光谱和时间区域中实时绘制频率和时间分辨瞬态吸光度。