Nakamura Kazuki, Guérin Laurent, Privault Gaël, Nakabayashi Koji, Hervé Marius, Collet Eric, Ohkoshi Shin-Ichi
Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.
DYNACOM IRL2015 University of Tokyo - CNRS - Université de Rennes, Department of Chemistry, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.
Nat Commun. 2025 Jun 6;16(1):5012. doi: 10.1038/s41467-025-60401-4.
In materials exhibiting photoinduced phase transitions, and in which both charge transfer and spin transitions occur, there has long been a debate about which process drives the phase transition. Herein, we present experimental evidence supporting an optically charge-transfer-induced spin transition (CTIST) process, as demonstrated through femtosecond optical spectroscopy in two-dimensional cyanido-bridged cobalt-tungstate photomagnets. Optical and magnetic studies revealed that the photoexcitation of the ground low-temperature (LT) Co-W state leads to a photoinduced phase transition towards the Co-W state, which is similar to the high temperature (HT) state. Ultrafast spectroscopy further indicates that this optical excitation of the intermetallic W-to-Co charge-transfer band produces a transient photoexcited (PE) Co-W state, which decays within 130 fs through a spin transition towards the Co-W state. Here we show that the CTIST dynamics corresponds to the Co-W (LT) → Co-W (PE) → Co-W (HT) sequence. The present work sheds a new light on understanding optical dynamics underlying the photoinduced phase transitions.
在呈现光致相变且同时发生电荷转移和自旋转变的材料中，关于哪个过程驱动相变一直存在争论。在此，我们展示了支持光致电荷转移诱导自旋转变（CTIST）过程的实验证据，这是通过对二维氰基桥联钴钨酸盐光磁体进行飞秒光谱学研究得以证明的。光学和磁性研究表明，基态低温（LT）Co-W态的光激发会导致向Co-W态的光致相变，该态类似于高温（HT）态。超快光谱学进一步表明，金属间W到Co电荷转移带的这种光激发产生了一个瞬态光激发（PE）Co-W态，它通过向Co-W态的自旋转变在130飞秒内衰减。在此我们表明，CTIST动力学对应于Co-W（LT）→Co-W（PE）→Co-W（HT）序列。本工作为理解光致相变背后的光学动力学提供了新的思路。
