Electronic structure and phonons of low-dimensional metals prepared on crystal surfaces

在低维金属中，电子-电子和电子-声子相互作用等效应在产生密度波和超导性等有趣现象方面起着重要作用。光电子能谱提供了单粒子谱函数，因此在低维物理中是一种强有力的技术。本工作的目的是利用角分辨光电子能谱（ARPES）研究表面制备的低维结构的电子性质，并利用超高分辨电子能量损失能谱（UREELS）研究这种材料的声子色散，最终揭示表面新现象和有趣现象的机制。In/Cu(001) CDW体系中CDW间隙的费米学和温度依赖性表现为弱耦合样，但这与相变的其他定性特征相矛盾。因此，我们测量了相变过程中的临界x射线散射。通过分析二维Ising相变以上的晶格相关长度，并将其与ARPES获得的CDW相关长度进行比较，我们成功地将相变分类为强耦合、长相干型，这是通常不为人知的。这是这项工作最重要的成果。我们还研究了超薄Mn-Pd表面合金的磁性和空位构型熵驱动下银（001）上Bi单层的新相变。在后一项研究中，我们在Bi/Ag（001）中发现了一个巨大的Rashba自旋轨道分裂，其大小几乎比之前已知的大一个数量级。目前正在对这一现象进行研究。

In low-dimensional metals, the effects interactions, such as electron-electron and electron-phonon ones, plays significant roles to give rise to intriguing phenomena such as density waves and superconductivity. Photoelectron spectroscopy provides single-particle spectral functions and hence serves as a powerful technique in low-dimensional physics. The aim of this work was to study electronic properties of low-dimensional structures prepared on surfaces by angle-resolved photoelectron spectroscopy (ARPES) and to study phonon dispersion of such materials by ultrahigh resolution electron energy loss spectroscopy (UREELS), and eventually to reveal the mechanisms of new and interesting phenomena at surfaces. The Fermiology and the temperature dependence of a CDW gap on In/Cu(001) CDW system exhibited weak-coupling-like appearance, which however contradicted with other qualitative characteristics of the phase transition. We therefore measured the critical X-ray scattering during the phase transition. By analyzing the lattice correlation length above the 2D Ising transition and comparing it with the CDW correlation length obtained by ARPES, we have succeeded in categorizing the phase transition to a strong-coupling, long-coherence type, which usually was not known. This is the most significant achievement of this work. We also studied the magnetism of ultrathin Mn-Pd surface alloys and novel phase transition in Bi monolayer on Ag(001) driven by vacancy-configuration entropy. During the latter study, we found a giant Rashba spin-orbit splitting in Bi/Ag(001), which is nearly an order of magnitude larger than those previously known. The study of this phenomenon is currently under way.