The nonequilibrium (NEQ) excitonic-insulator (EI) phase is a dynamical state of matter for excited insulators or semiconductors, and it is characterized by self-sustained coherent oscillations of the excitonic condensate. In this Rapid Communication we highlight the main qualitative features of a NEQ-EI time- and angle-resolved photoemission spectroscopy (tr-ARPES) spectrum. We show that monochromatic probes yield a steady-state spectrum with excitonic structures originating from the dressing of conduction states with the coherent condensate. These structures are replicas of the NEQ valence bands but shifted upward in energy by the condensate frequency. Reducing the probe duration below the condensate period, the band structure gradually fades away and the tr-ARPES signal becomes proportional to the excitonic wave function. In addition, the signal amplitude becomes periodic in the impinging time of the probe, with the same period of the oscillating condensate.

中文翻译：

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非平衡激子绝缘子的时间分辨ARPES谱：揭示超短脉冲的宏观相干性

非平衡（NEQ）激子绝缘体（EI）相是受激绝缘体或半导体的动态物质状态，其特征在于激子冷凝物的自持相干振荡。在本快速通讯中，我们重点介绍了NEQ-EI时间和角度分辨光发射光谱（tr-ARPES）光谱的主要定性特征。我们证明了单色探针会产生稳态具有激子结构的光谱，其源自相干冷凝物的导电态的修整。这些结构是NEQ价带的复制品，但在能量上因冷凝频率向上移动。将探测持续时间减少至凝结期以下，能带结构逐渐消失，tr-ARPES信号与激子波函数成比例。此外，信号振幅在探头的撞击时间内变为周期性，并具有相同的振荡冷凝水周期。