光学泵浦激子稠密系综向电荷转移态的非均匀演化
Inhomogeneous Evolution of a Dense Ensemble of Optically Pumped Excitons to a Charge Transfer State
AI总结：
本文提出半唯象模型，描述光学激子与序参量交织时的时空效应，揭示激子自陷提高密度触发相变，使系统分层为通过动力学相变演化的畴。
摘要：
短光脉冲诱导的相变是合作电子态动力学研究中的主流方向。本文提出了一种半唯象模型，用于描述当光学激子与序参量相互交织时（例如在具有中性-离子铁电相变的有机化合物中）预期的时空效应。这里出现了一个概念上的复杂性，即激发态和基态的有序性都源于分子间的电子转移。为了在相同的根源上描述热力学和动力学效应，我们将相变视为激子绝缘体（Excitonic Insulator）——一种在激子能量变为负值时出现的半导体假想相。在初始泵浦脉冲之后，激子的准凝聚体可以作为宏观量子态出现，随后在与其他易受不稳定性影响的自由度相互作用时发生演化。激子的自陷效应提高了其密度，该密度可以在局部超过临界值，从而触发相变。系统被分层为多个畴，这些畴通过动力学相变演化，甚至在引发相变的初始激子复合后仍可能持续存在。
英文摘要：
Phase transformations induced by short optical pulses are mainstream in studies on the dynamics of cooperative electronic states. We present a semi-phenomenological modeling of spacio-temporal effects expected when optical excitons are intricate with the order parameter as in, e.g., organic compounds with neutral-ionic ferroelectric phase transitions. A conceptual complication appears here, where both the excitation and the ground state ordering are built from the intermolecular electronic transfer. To describe both thermodynamic and dynamic effects on the same root, we adopt, for the phase transition, a view of the Excitonic Insulator - a hypothetical phase of a semiconductor that appears if the exciton energy becomes negative. After the initial pumping pulse, a quasi-condensate of excitons can appear as a macroscopic quantum state that then evolves, while interacting with other degrees of freedom which are prone to an instability. The self-trapping of excitons enhances their density, which can locally surpass a critical value to trigger the phase transformation. The system is stratified in domains that evolve through dynamical phase transitions and may persist even after the initiating excitons have recombined.
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