论文标题
密切相关的激子绝缘子中的临界电荷波动和出现的连贯性
Critical charge fluctuations and emergent coherence in a strongly correlated excitonic insulator
论文作者
论文摘要
激子绝缘子是一个连贯的电子相，它是由结合粒子孔对的宏观群体形成的 - 激子。只有少数已知的候选材料，集体激发行为挑战，被晶格效应所掩盖。在这里，我们使用偏振分辨的拉曼光谱法在候选零间隙半导体ta $ _2 $ _2 $ _5 $ _5 $中揭示了四极性激子模式，将其从晶格呼射子中解散。激音模式明显地柔软接近相变，显示其电子特征，而其与非关键晶格模式的耦合显示可增强过渡温度。在冷却时，我们观察到在相关的绝缘体间隙边缘，带状态相干叠加的逐渐出现，与平均场理论预测有很大的偏离。我们的结果表明，在平衡体积材料中实现了强相关的激子状态。
Excitonic insulator is a coherent electronic phase that results from the formation of a macroscopic population of bound particle-hole pairs - excitons. With only a few candidate materials known, the collective excitonic behavior is challenging to observe, being obscured by crystalline lattice effects. Here we use polarization-resolved Raman spectroscopy to reveal the quadrupolar excitonic mode in the candidate zero-gap semiconductor Ta$_2$NiSe$_5$ disentangling it from the lattice phonons. The excitonic mode pronouncedly softens close to the phase transition, showing its electronic character, while its coupling to non-critical lattice modes is shown to enhance the transition temperature. On cooling, we observe the gradual emergence of coherent superpositions of band states at the correlated insulator gap edge, with strong departures from mean-field theory predictions. Our results demonstrate the realization of a strongly correlated excitonic state in an equilibrium bulk material.
