NSF-BSF: Spectroscopy of excitonic insulators with direct gap

非技术摘要：组成材料的颗粒之间的相互作用可能会导致令人惊讶的结果，其中材料作为一个整体的性质与其组分的性质不同。所讨论的粒子可以是电子或电子空穴，它们是材料原子晶格中缺少的电子。材料中电子和空穴之间的相互作用可以导致这种新性质的出现-凝聚态物理学积极探索的前沿。这种有趣的材料的一个例子是激子绝缘体，激子是由于电子和空穴之间的吸引力相互作用而出现在材料中的新粒子状实体。这种激子有望在足够低的温度下达到一种新的量子态，称为“激子凝聚体”。关于它存在的理论预言从未被确凿的实验证据完全证实。本文的工作旨在为激子凝聚提供直接而令人信服的证据。该项目还为博士后和本科生提供低温高分辨率光谱学方面的全面培训，他们将受益于国际合作努力带来的经验。技术摘要：Rutgers-Technion NSF-BSF合作探索了导致固体中激子绝缘体难以捉摸状态的条件，通过采用传输，角分辨光电发射（ARPES）和偏振分辨光散射（拉曼）光谱的组合，同时研究这种状态的性质和动力学。我们的目标是得到完整的相图激子绝缘体，其中包括一个结构不稳定性交织在一起的半金属到绝缘体的过渡，并建立合理的不同制度的激子凝聚，确定潜在的微观机制，并测试相关的理论。从这项研究中获得的经验教训将进一步促进对其他强相互作用量子系统中自组织的更广泛理解。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Nontechnical Abstract:Interactions between particles making up a material can lead to surprising consequences, where the properties of the material as a whole are distinct from the properties of its constituents. The particles in question can be electrons, or electron holes, which are missing electrons in the material's atomic lattice. Interactions between electrons and holes in materials can lead to the emergence of such new properties – a frontier actively explored by condensed matter physics. An example of such interesting material is the excitonic insulator, with excitons being new particle-like entities in the material that appear due to the attractive interaction between electrons and holes. Such excitons are expected to achieve a novel quantum state, called "excitonic condensate" at sufficiently low temperatures. Theoretical predictions of its existence have never been fully confirmed by conclusive experimental evidence. This work aims at providing direct and convincing evidence for the excitonic condensate. This project also provides comprehensive training to postdocs and undergraduate students in low-temperature high-resolution spectroscopies, who will benefit from experiences brought by international collaborative efforts.Technical Abstract:The Rutgers-Technion NSF-BSF collaboration explores the conditions leading to the elusive state of excitonic insulator in solids by employing a combination of transport, angle-resolved photoemission (ARPES) and polarization-resolved light scattering (Raman) spectroscopies to concurrently study the properties and the dynamics of this state. The objective is to to derive the complete phase diagram for excitonic insulators that includes a structural instability intertwined with a semimetal-to-insulator transition and to establish plausible distinct regimes of the exciton condensation, identify the underlying microscopic mechanisms, and test the relevant theories. The lessons learned from this study will further promote broader understanding of self-organization in other strongly interacting quantum systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.