准一维金属原子链的量子相变研究

Quasi-one-dimensional metal atomic chains tend to experience Peierls-like transition with doubling their lattice constants, forming charge density waves (CDW) and opening energy gaps near the Fermi surface, and even to exhibit spin-charge separation due to their Fermi surface nesting and the electron-lattice interaction. Due to its simplicity, atomic chains can be strictly studied theoretically. But so far neither the theory based on single-electron approximation nor that based on Luttinger liquid model can well explain the whole picture of all experiments. So it is of fundamental significance to shed light on the various mechanisms by observing the change of their crystal structure and electronic structure in the phase transition. In this project, we propose to prepare a new kind of atomic chains on stepped Si and Ge surface using MBE, then investigate their atomic and electronic structures using scanning tunneling microscope (STM), angle-resolved photoemission spectroscopy (ARPES) and synchrotron radiation based surface x-ray diffraction (SXRD). We will explain the phase transition temperature deviation both from BCS theory and from Luttinger liquid theory by considering various mechanisms in the model calculations. This research is expected to reveal the effect of strong spin-orbit coupling on 1D phase transiton and deepen our understanding of the role of various mechanisms in quantum phase transition, which is of great significance both to developing fundamental solid state physics theory and to designing quantum devices.

准一维金属原子链因其平行费米面嵌套和电子－晶格相互作用而易于发生类 Peierls 相变，其晶格常数加倍，形成电荷密度波，费米面附近出现能隙，甚至发生自旋－电荷分离；其相变机理可进行严格的理论解析研究，但目前无论是单电子近似理论还是 Luttinger 液体理论都不能很好地解释全部实验现象。因此，研究一维原子链的晶格结构和电子结构在相变中的变化规律和各种作用机制就具有基础上的重要性，并已成为固体理论的新知识增长点。本项目拟采用分子束外延技术，在Si、Ge台阶表面上制备自组装 Bi 原子链，随后采用扫描隧道显微镜、角分辨光电子能谱和同步辐射表面X射线衍射技术研究该体系在相变中的晶体结构和电子结构的变化，结合各种相互作用的模型计算找出导致相变温度偏离 BCS 理论和 Luttinger 理论的作用机理，揭示自旋－轨道耦合对相变的影响，这对固体理论的发展和量子器件的设计都具有重要意义。