The Verwey transition in magnetite (Fe₃O₄) is the first metal–insulator transition ever observed¹ and involves a concomitant structural rearrangement and charge–orbital ordering. Owing to the complex interplay of these intertwined degrees of freedom, a complete characterization of the low-temperature phase of magnetite and the mechanism driving the transition have long remained elusive. It was demonstrated in recent years that the fundamental building blocks of the charge-ordered structure are three-site small polarons called trimerons². However, electronic collective modes of this trimeron order have not been detected to date, and thus an understanding of the dynamics of the Verwey transition from an electronic point of view is still lacking. Here, we discover spectroscopic signatures of the low-energy electronic excitations of the trimeron network using terahertz light. By driving these modes coherently with an ultrashort laser pulse, we reveal their critical softening and hence demonstrate their direct involvement in the Verwey transition. These findings shed new light on the cooperative mechanism at the origin of magnetite’s exotic ground state.

磁铁矿 (Fe ₃ O ₄ ) 中的 Verwey 跃迁是有史以来观察到的第一个金属-绝缘体跃迁¹，并且涉及伴随的结构重排和电荷-轨道排序。由于这些相互交织的自由度之间的复杂相互作用，长期以来，对磁铁矿低温相的完整表征和驱动转变的机制一直难以捉摸。近年来已经证明，电荷有序结构的基本组成部分是三点小极化子，称为三聚体². 然而，迄今为止尚未检测到这种三聚体顺序的电子集体模式，因此仍然缺乏从电子角度理解 Verwey 跃迁的动力学。在这里，我们使用太赫兹光发现了三聚体网络的低能电子激发的光谱特征。通过用超短激光脉冲连贯地驱动这些模式，我们揭示了它们的临界软化，从而证明了它们直接参与了 Verwey 跃迁。这些发现为磁铁矿奇特基态起源的合作机制提供了新的线索。