Ca$_2$RuO$_4$中相干声子诱导的隐藏四极有序态
A coherent phonon-induced hidden quadrupolar ordered state in Ca$_2$RuO$_4$
AI总结：
本研究提出通过相干激发与序参量强耦合的声子，在Ca$_2$RuO$_4$中诱导热禁戒的自旋-轨道纠缠四极有序态的动力学转变，结合光谱测量与理论计算验证该转变，并为揭示和调控隐藏多极有序态提供通用途径。
摘要：
超快激光激发提供了一种瞬态实现热平衡下隐藏的长程有序电子物态的途径。近期，该方法已在强关联材料中揭示了多种热不可达的有序态，包括电荷密度波、铁电、磁性以及交织的电荷-轨道有序态。然而，由于用光直接操控和探测的难度，表现出更高多极有序的更奇异隐藏态仍难以被发现。本研究中，我们展示了一种方法：通过相干激发与序参量强耦合的声子，在Ca$_2$RuO$_4$中诱导从热允许到热禁戒的自旋-轨道纠缠四极有序态的动力学转变。结合探测光子能量分辨的相干声子光谱测量与模型哈密顿量计算，我们表明该动力学转变通过强耦合声子的温度、泵浦激发通量及探测光子能量依赖关系中的异常现象得以体现。通过这一过程，我们为揭示隐藏多极有序态并在超短时间尺度上调控其重定向提供了一条通用途径。
英文摘要：
Ultrafast laser excitation provides a means to transiently realize long-range ordered electronic states of matter that are hidden in thermal equilibrium. Recently, this approach has unveiled a variety of thermally inaccessible ordered states in strongly correlated materials, including charge density wave, ferroelectric, magnetic, and intertwined charge-orbital ordered states. However, more exotic hidden states exhibiting higher multipolar ordering remain elusive owing to the challenge of directly manipulating and detecting them with light. Here we demonstrate a method to induce a dynamical transition from a thermally allowed to a thermally forbidden spin-orbit entangled quadrupolar ordered state in Ca$_2$RuO$_4$ by coherently exciting a phonon that is strongly coupled to the order parameter. Combining probe photon energy-resolved coherent phonon spectroscopy measurements with model Hamiltonian calculations, we show that the dynamical transition is manifested through anomalies in the temperature, pump excitation fluence, and probe photon energy dependence of the strongly coupled phonon. With this procedure, we introduce a general pathway to uncover hidden multipolar ordered states and to control their re-orientation on ultrashort timescales.
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