过渡金属硫族化合物栅控量子点中自旋-能谷态的研究

Spin-valley degree of freedom in two-dimensional semiconducting transition metal dichalcogenides (TMDCs), not only contains rich physics, but also can be used for quantum computation. Researches on spin-valley states in TMDCs become one of the most exciting research areas in condensed matter physics and materials science. Studies on such spin-valley states in TMDCs-based electronic devices remain challenging due to technical difficulties dealing with Ohmic contacts, impurities and disorders at interface. Based on previous studies, we plan to use h-BN encapsulation to fabricate high quality gate-defined quantum dots on TMDCs to overcome the limitation induced by Ohmic contacts, impurities and disorders at interface. We propose investigations on spin-valley states in TMDCs gate-defined quantum dots. Design of multiple-layer overlapping electrodes will be tested to ensure a smaller confining potential, allowing gate-defined quantum dots enter into few-carrier regime. Energy level diagram of spin-valley states will be mapped. Properties of spin-valley states, such as spin-valley splitting, g factor, will be measured. By tuning spin-valley blockade using magnetic field and gate voltage, we can investigate coupling mechanism of spin, valley, orbit degree of freedom. This project will not only pave the way for a deeper understanding in spin-valley related physics, but also shed light on possible applications of quantum computation based on spin-valley degree of freedom.

二维半导体过渡金属硫族化合物（TMDCs）中的自旋-能谷自由度，不仅蕴含丰富的物理，还可用来编码进行量子计算，是凝聚态物理、材料科学研究的热点之一。受界面杂质缺陷密度、源漏电极欧姆接触质量等因素的限制，对TMDCs电学器件中自旋-能谷态的研究充满挑战。本项目拟在前期研究基础上，利用氮化硼包裹工艺制备高质量TMDCs栅控量子点器件，以克服界面杂质缺陷密度和欧姆接触质量对器件的限制，实现对TMDCs栅控量子点中自旋-能谷态的实验研究：摸索多层交叉电极工艺，缩小束缚势场，实现栅控量子点少载流子填充；标定自旋-能谷态能级排布，提取自旋-能谷劈裂、g因子等自旋-能谷态信息；利用不同磁场、电极电压对自旋-能谷阻塞效应进行调节，研究TMDCs自旋、能谷、轨道自由度的耦合机制。本项目的开展将有助于加深对自旋-能谷态相关物理问题的理解，也是对利用自旋-能谷自由度进行量子计算的有益探索。

以过渡金属硫族化合物、石墨烯等为代表的具有六方晶格的二维材料，可以承载能谷自由度。这一物理自由度与自旋类似，可被外场调控，用来编码信息。因而，对这些自旋-能谷态的研究既是凝聚态物理、材料科学研究的热点，也是量子信息领域密切关注的方向。另一方面，可以束缚单个电子的栅控量子点器件，提供了在单粒子层面利用电学手段研究材料性质的有力平台，同时也被视为实现量子计算的可行方案之一。本项目的研究内容就是利用栅控量子点这一高度可调的器件平台，对二维材料中的自旋、能谷自由度开展研究，探索其在量子信息中的潜在应用。围绕这一研究内容，我们取得了如下创新性成果：1.实现了高质量栅控量子点的制备，成功调节量子点进入少电子区，并完成了对前36个填充电子数的分辨；2.实现了对自旋-能谷态的标定，确定了低激发态自旋-能谷态的填充顺序，测量了自旋g因子（~2）和能谷g因子（~18），表征了自旋轨道耦合能隙的大小（~60μeV）；3.实现了对自旋-能谷自由度的调控，通过外加磁场调节自旋-能谷态劈裂的大小，完成了利用外加垂直电场控制迷你能谷自由度，从而调控量子点中电子自旋的填充顺序。在项目资助下，在Nat. Commun., PNAS等重要学术期刊上发表sci论文6篇，同时申请发明专利2项。这些研究成果促进了对二维材料中自旋、能谷自由度物理机制的理解，同时也推动了二维材料量子信息器件研究的发展。