Abstract：
We study by femtosecond infrared spectroscopy the ultrafast and persistent photoinduced phase transition of the Rb0.94Mn0.94Co0.06[Fe(CN)6]0.98∙0.2H2O material, induced at room temperature by a single laser shot. This system exhibits a charge-transfer based phase transition with a 75 K wide thermal hysteresis, centred at room temperature, from the low temperature Mn3+-N-C-Fe2+ tetragonal phase to the high temperature Mn2+-N-C-Fe3+ cubic phase. At room temperature, the photoinduced phase transition is persistent. However, the out-of-equilibrium dynamics leading to this phase is multi-scale. Femtosecond infrared spectroscopy, particularly sensitive to local reorganizations through the evolution of the frequency of the N-C vibration modes with the different characteristic electronic states, reveals that at low laser fluence and on short time scale, the photoexcitation of the Mn3+-N-C-Fe2+ phase creates small charge-transfer polarons [Mn2+-N-C-Fe3+]* within ≃ 250 fs. The local trapping of photoinduced intermetallic charge-transfer is characterized by the appearance of a polaronic infrared band, due to the surrounding Mn2+-N-C-Fe2+ species. Above a threshold fluence, when a critical fraction of small CT-polarons is reached, the macroscopic phase transition to the persistent Mn2+-N-C-Fe3+ cubic phase occurs within ≃ 100 ps. This non-linear photo-response results from elastic cooperativity, intrinsic to a switchable lattice and reminiscent of a feedback mechanism.
摘要：
我们通过飞秒红外光谱研究了Rb0.94Mn0.94Co0.06[Fe（CN）6]0.98*0.2H2O材料的超快和持久的光诱导相变，在室温下由单个激光发射诱导。该系统具有基于电荷转移的相变，具有75K宽的热滞后，以室温为中心，由低温Mn3+-N-C-Fe2+四方相转变为高温Mn2+-N-C-Fe3+立方相。在室温下,光致相变是持久的。然而,导致这一阶段的失衡动力学是多尺度的。飞秒红外光谱,通过具有不同特征电子状态的N-C振动模式的频率演变，对局部重组特别敏感，揭示了在低激光通量和短时间尺度下，Mn3-N-C-Fe2相的光激发会在250fs内产生小的电荷转移极化子[Mn2-N-C-Fe3]*。光诱导的金属间电荷转移的局部捕获的特征在于极化红外波段的出现，由于周围的Mn2-N-C-Fe2物种。超过阈值通量，当达到小CT极化子的临界分数时，宏观相变到持久性Mn2-N-C-Fe3立方相发生在100ps内。这种非线性光响应是弹性协同性的结果，可切换晶格固有的，让人想起反馈机制。
