Solid-liquid transition and intermediate state formation in strongly correlated 2D systems

理解具有强电子-电子相互作用的二维（2D）电子系统中的基态和相变一直是凝聚态物理学中一个尚未解决的中心问题。除了2D电子之间的强相关性之外，该问题的另一个挑战是真实的材料中不可避免地存在无序。最近的理论研究表明，在二维系统中，当粒子间的相互作用较强而无序较弱时，在液态和固态之间可能存在新的中间电子相。然而，在实验中是否存在这种新的物质中间态还远不清楚。该项目的目标是提供新的见解，通过对最先进的最高纯度样品进行新的传输测量，帮助解决基础物理学中的这一挑战性问题。通过这项研究所获得的结果具有更广泛的意义，更深入地了解相关的凝聚态系统一般。此外，该项目作为一个有价值的平台，教育研究生和本科生，并在凝聚态和半导体物理学的前沿研究拓展大学预科生。参加该项目的学生将接受低温学、低温实验、信号和数据分析以及半导体加工和制造方面的培训。这些研究经验和技能，预计准备年轻学生继续在学术界或工业界的成功职业生涯。技术摘要该项目旨在通过对最先进的半导体砷化镓2D异质结构进行新的电子和热电输运实验，揭示半导体量子结构中强相关二维（2D）载流子的性质。本论文的研究范围主要包括库仑相互作用驱动的二维关联空穴或电子系统中费米液体到维格纳固体的相变。过去，在强磁场的存在下，已经发现了二维电子的各种多体量子液相和固相。然而，在实验中很少有人知道量子2D维格纳固体如何转化为液相时，磁场是小的或不存在的，尽管有很多理论的兴趣和研究。在这个项目中，互补的电子和热电（熵）输运技术被用来阐明在强关联的二维载流子系统中弱无序的二维液-固转变，并探索库仑相互作用效应驱动的新的中间相的出现，正如许多理论研究所预测的那样。

Nontechnical abstractUnderstanding the ground states and phase transitions in two-dimensional(2D) electronic systems with strong electron-electron interactions has been a central unsettled problem in condensed matter physics. In addition to the strong correlations between 2D electrons, a further challenge in the problem is the unavoidable presence of disorder in real materials. Recent theoretical studies suggest that novel intermediate electronic phases might exist between the liquid and solid states in 2D systems when the interactions between particles are strong and the disorder is weak. However, it is far from clear whether such new intermediate states of matter exist in experiments. The goal of this project is to provide new insights to help unraveling this challenging problem in fundamental physics through new transport measurements on state-of-the-art samples with the highest purity. The results obtained through this research have broader implications to the deeper understanding of correlated condensed matter systems in general. Moreover, the project serves as a valuable platform to educate graduate and undergraduate students, and outreach pre-college students on cutting edge research in condensed matter and semiconductor physics. Student participants in the project receive hands on training in cryogenics, low temperature experimentation, signal and data analysis, and semiconductor processing and fabrication. These research experiences and skills are expected to prepare young students for continuing a successful career in either academia or industry. Technical abstractThe project aims to shed new light on the nature of strongly correlated two-dimensional (2D) carriers in semiconductor quantum structures through new electronic and thermoelectric transport experiments on state-of-the-art semiconductor gallium arsenide 2D heterostructures. The scope of this research mainly encompasses the study of the Coulomb interaction driven 2D Fermi liquid to Wigner solid phase transition in correlated 2D hole or electron systems. In the past, various many-body quantum liquid and solid phases of 2D electrons have been found in the presence of a strong magnetic field. However, very little is known in experiment about how the quantum 2D Wigner solid transforms into the liquid phase when the magnetic field is small or absent, despite much theoretical interests and investigations. In this project, complementary electronic and thermoelectric (entropic) transport techniques are employed to elucidate the 2D liquid-solid transition in strongly correlated 2D carrier systems with weak disorder, and explore the emergence of new intermediate phase(s) driven by Coulomb interaction effects, as predicted in a number of theoretical studies.