磁铁矿中三重子序软电子模的发现
Discovery of the soft electronic modes of the trimeron order in magnetite
摘要：
磁铁矿（Fe $_3$ O $_4$）中的Verwey转变是第一个被观察到的金属-绝缘体转变，它涉及到伴随的结构重排和电荷轨道有序。由于这些相互交织的自由度的复杂相互作用，磁铁矿的低温相的完整表征和驱动转变的机制长期以来一直难以捉摸。近年来，电荷有序结构的基本组成部分是三位小极化子，称为三分子。然而，电子集体模式，这三聚体秩序尚未被检测到的日期，因此，从电子的角度来看，仍然缺乏对动力学的Verwey过渡的理解。在这里，我们发现的低能量电子激发的三聚体网络使用太赫兹光的光谱签名。通过用超短激光脉冲相干驱动这些模式，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转变。这些发现代表了第一次观察到的软模式磁铁矿和新的光在其异国情调的基态起源的合作机制。
英文摘要：
The Verwey transition in magnetite (Fe$_3$O$_4$) is the first metal-insulator transition ever observed and involves a concomitant structural rearrangement and charge-orbital ordering. Due 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 trimerons. 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 represent the first observation of soft modes in magnetite and shed new light on the cooperative mechanism at the origin of its exotic ground state.
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