Symmetry breaking across phase transitions often causes changes in selection rules and emergence of optical modes which can be detected via spectroscopic techniques or generated coherently in pump-probe experiments. In second-order or weakly first-order transitions, fluctuations of the ordering field are present above the ordering temperature, giving rise to intriguing precursor phenomena, such as critical opalescence. Here, we demonstrate that in magnetite $\left({\mathrm{Fe}}_3{\mathrm{O}}_4\right)$ light excitation couples to the critical fluctuations of the charge order and coherently generates structural modes of the ordered phase above the critical temperature of the Verwey transition. Our findings are obtained by detecting coherent oscillations of the optical constants through ultrafast broadband spectroscopy and analyzing their dependence on temperature. To unveil the coupling between the structural modes and the electronic excitations, at the origin of the Verwey transition, we combine our results from pump-probe experiments with spontaneous Raman scattering data and theoretical calculations of both the phonon dispersion curves and the optical constants. Our methodology represents an effective tool to study the real-time dynamics of critical fluctuations across phase transitions.

中文翻译：

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磁铁矿中光诱导的电子-声子相互作用相干产生对称禁带声子

跨越相变的对称性破裂通常会导致选择规则发生变化，并出现光学模式，可以通过光谱技术检测到这种现象，或者在泵浦探针实验中相干地产生这种光学模式。在二阶或弱一阶跃迁中，有序场的波动会出现在有序温度之上，从而引起有趣的前体现象，例如临界乳光。在这里，我们证明了在磁铁矿中$（{铁}_3{\mathrm{Ø}}_4）$光激发耦合到电荷阶跃的临界波动，并在Verwey转变的临界温度以上相干地生成有序相的结构模式。我们的发现是通过超快速宽带光谱法检测光学常数的相干振荡并分析其对温度的依赖性而获得的。为了揭示Verwey跃迁起源处结构模式与电子激发之间的耦合，我们将泵浦探针实验的结果与自发拉曼散射数据以及声子色散曲线和光学常数的理论计算相结合。我们的方法论是研究跨相变临界波动的实时动态的有效工具。