MoWSe_Spin and pseudospin properties of energetically controllable dark and bright excitons in tailored Mo1-xWxSe2 alloys

二维过渡金属二卤化物，其层状结构允许在室温下也存在异常强束缚的激子，具有独特的自旋和谷伪自旋特征，这可能导致纳米光子学和自旋基纳电子学的高度激发和新颖的物理。为了充分发挥这一新材料体系的潜力，并使人们能够定制这些纳米材料的功能和结构性质，必须回答关于其单分子膜中激子的关键问题。为此，我们重点研究了新型Mo1-xWxSe2合金中光学亮K谷激子和暗K谷激子之间的相互作用。这些机械剥离的合金的成分依赖性将使我们能够在很大范围内调节A和B激子自旋态的能量，从而导致暗激子和亮激子的混合。利用具有可调谐导带能级和价带能级的MO1-xWxSe2结构，我们有望对自旋和谷伪自旋的性质和动力学提供新的和彻底的见解，这将在可调激子和载流子交换相互作用和自旋-轨道耦合以及激子与周围槽的相互作用方面进行研究。后者不仅包括核自旋和声子，还包括缺陷、衬底材料和单层几何结构。光学检测磁共振技术与共振和偏振激光激发以及微米空间分辨率相结合，将允许对基于自旋的激子属性进行磁共振成像，从而向基于自旋的量子信息设备和传感器技术迈出一步。除了暗激子和亮激子能量与组成有关的可控性外，我们还将对衬底材料施加单轴和双轴应变，以微调自旋态能量，操纵电子特别是空穴的自旋-轨道耦合，并改变对称条件。对K谷激子和伽马谷激子的比较研究将进一步加强对自旋和多载流子物理的理解，在定制的MO1-xWxSe2结构中利用可变功率的高能激光激发。

Two-dimensional transition metal dichalcogenides, whose layered structure allows for unusually strongly bound excitons existing even at room temperature, possess unique spin and valley pseudospin features that may give rise to highly exciting and novel physics for the nanophotonics as well as spin-based nanoelectronics. In order to exploit the full potential of this new material system and to allow one to tailor the functional and structural properties of these nanomaterials, key open questions regarding the excitons in their monolayers have to be answered.For that purpose, we focus on the interaction between optically bright and dark K-valley excitons in novel Mo1-xWxSe2 alloys. The composition dependence of these mechanically exfoliated alloys shall allow us to tune the energies of the A- and B-exciton spin states, also leading to a dark- and bright-exciton mixing, in a wide range. Using the Mo1-xWxSe2 structures with tunable conduction- and valence-band levels, we expect to provide novel and thorough insights into the spin and valley pseudospin properties and dynamics, which shall be studied with regard to the tunable exciton and carrier exchange interactions and spin-orbit coupling as well as to the interaction of the excitons with the surrounding bath. The latter shall include not only nuclear spins and phonons, but also defects, substrate materials and the monolayer geometry. Optically detected magnetic resonance techniques combined with resonant and polarized laser excitation and micrometer spatial resolution shall allow for a magnetic resonance imaging of the spin-based exciton properties, thus making a step toward spin-based quantum information devices and sensor technologies. Besides the composition-dependent controllability of the dark and bright exciton energies, we will apply uni- and biaxial strain to the substrate material for fine-tuning the spin state energies, manipulating the spin-orbit coupling of the electrons and particularly holes and changing symmetry conditions. A comparative study of the K- and Gamma-valley excitons shall furthermore enhance the understanding of spin and many-carrier physics, by exploiting high-energy laser excitation with variable power, in the tailored Mo1-xWxSe2 structures.