Quasiparticle dynamics and optical properties of alkali metal doped few-layered transition metal dichalcogenides

本项目的目标是解开和工程的电子和光学性质，电子自旋和相关的多体效应在新的二维过渡金属二硫属化物（TMD），如MoSe 2。建议的工作包括原位样品合成和功能化和多光谱方法：一方面，自旋和角度相关的光电子能谱将被用来研究电子能带结构和重整化;另一方面，拉曼光谱将被用来研究振动特性和电子-声子耦合。我们可以设计物理性质的控制参数是：（1）层数，（2）堆叠，（3）合金化，（4）碱金属掺杂和（5）横向量子限制成纳米带。据信，这些参数允许广泛的调整的物理性质，包括一个完全自旋极化的电子能带结构，光学带隙，电荷密度波和超导制度。特别地，TMD的层数被期望控制自旋极化，因为奇数层不具有反转中心，因此具有完全自旋极化带。由于诸如MoSe 2的TMD的电子结构由具有相反自旋的两个谷组成，因此这些材料的载流子通常被设想为谷电子学的构建块。不同TMD的堆叠提供了一种具有非凡光电性能的新型异质结构。合金化（例如用W代替Mo或用S代替Se）预期产生对带隙的完全控制。碱金属掺杂将半导体TMD转变为金属，并且电荷载流子浓度（其可以由碱（ne）金属类型控制）决定电荷密度波或超导状态是否占主导地位。如果有可能在阶梯表面上生长TMD条带，则可以设计由谷依赖选择规则和区带折叠带组成的非常丰富的激发光谱。由于在态密度中存在范霍夫奇异性，最大吸收的能量可以通过带宽度来设计。所提出的建议的新颖方面涉及费米表面的自旋极化性质将如何影响重整化和散射率，探索掺杂剂（碱金属和碱土金属）的全宽度以及功能化和量子限制方面。所提出的工作的可行性是牢固地建立在提案人对掺杂的块状过渡金属化合物和石墨烯的角分辨光电发射工作以及最近通过分子束外延合成高质量样品的暴风雨般的发展之上的。建议的工作将提供一个深刻的理解，不仅是物理的TMD，但一般的二维材料。

The goal of the present project is to unravel and engineer the electronic and optical properties, the electronic spin and related many-body effects in novel two-dimensional transition metal dichalcogenides (TMDs), such as MoSe2. The suggested work comprises of in-situ sample synthesis and functionalization and a multispectroscopic approach: on the one hand, spin- and angle dependent photoemission spectroscopy will be employed in order to investigate the electron energy band structure and renormalizations; on the other hand Raman spectroscopy will be employed to investigate the vibrational properties and electron-phonon coupling. The control parameters by which we can engineer the physical properties are: (1) layer number, (2) stacking, (3) alloying (4) alkali metal doping and (5) lateral quantum confinement into nanoribbons. It is believed that these parameters allow for a wide tuning of the physical properties including a fully spin polarized electron energy band structure, optical bandgap, charge-density waves and superconducting regimes. In particular, the layer number of TMDs is expected to control the spin polarization since odd-numbered layers do not have an inversion center and hence have fully spin polarized bands. Since the electronic structure of TMDs such as MoSe2 consists of two valleys with opposite spin, the carriers these materials are often envisioned as building blocks for valleytronics. Stacking of the different TMDs provides a new type of heterostructure with extraordinary optoelectronic properties. Alloying (for example replacing Mo by W or replacing Se by S) is expected to yield full control over the bandgap. Alkali-metal doping turns semiconducting TMDs into metals and the charge carrier concentration (which can be controlled by alkali(ne) metal type) dictates whether charge density wave or superconducting regimes dominate. If it is possible to grow ribbons of TMDs on stepped surfaces, a very rich excitation spectrum consisting of valley dependent selection rules and zonefolded bands could be engineered. Due to the presence of van-Hove singularities in the density of states, the energy of the maximum absorption can be engineered by the ribbon width. The novel aspects of the suggested proposal are related to how the spin-polarized nature of the Fermi surface will affect the renormalization and scattering rates, exploring the full breadth of dopants (alkali and alkaline earth) and on the functionalization and quantum confinement aspects. The proposed work's feasibility is firmly grounded on the proposers' angle-resolved photoemission work on doped bulk transition metal compounds and graphene and the recent stormy developments in high-quality sample synthesis by molecular beam epitaxy. The suggested work will provide a deep understanding, not only of the physics of TMDs but of two-dimensional materials in general.