Coulomb Blockade and Few-Electron Energy Spectra of Quantum Rings

这个凝聚态物理项目涉及具有圆形，即“环”几何形状的纳米级量子导体。理想的量子环具有许多迷人的特性：基态持续电流，强Aharonov-Bohm干涉效应，波函数和所有热力学量对封闭磁通的振荡依赖，周期由磁通量子给定。本研究将重点研究在少电子和库仑封锁体制下单个和多重连接的量子环的性质。PI最近发现，在足够小的Si/SiGe量子点中，非均匀应变松弛导致环状约束。此外，隧道测量证实了预期的通量量子周期性。在控制器件几何结构的前提下，将制备椭圆环和耦合环结构，并测量由零载流子占据的载流子填充的少载流子能谱、自旋相互作用和库仑封锁效应。这项工作将与最先进的有限元固体力学模拟相结合。实验数据将为纳米结构中电子和机械性能之间的相互作用提供反馈。参与这项研究的研究生将获得完整的技能，从深亚微米制造，到低温，低信号测量，再到数值模拟，这将为他们在学术界，半导体行业或政府工作做好准备。本项目的教学计划重点是改进电气工程专业核心课程的本科教学。在理想量子环中，载流子沿着圆轨道运行而不散射，具有迷人的特性：无阻力流动的电流、相位干涉效应，以及载流子能量和波函数对封闭磁通量的振荡依赖。量子环也被认为是量子计算的可能组成部分。这项研究将集中在单个和多重连接的量子环在少电子和库仑封锁制度下的性质，其中一个载流子绕环影响另一个隧道进入环的概率。所讨论的环源于蚀刻结构侧壁的应变松弛，使得控制系统的几何形状（圆形或椭圆形）和拓扑结构（单环或多环连接）成为可能。隧道电流测量将研究载流子和自旋相互作用，因为这些环是由从零开始的载流子填充的；结果将与最先进的有限元应变模拟进行比较，我们的数据将为纳米结构的电子和机械性能之间的相互作用提供实验反馈。参与这项研究的研究生将获得完整的技能，为他们在学术界，半导体行业或政府的研究工作做好准备。一个教学计划的重点是改进电气工程专业核心课程的本科教学是该项目的一个组成部分。

This Condensed Matter Physics project deals with nanoscale quantum conductors that have a circular, i. e., "ring" geometry. Ideal quantum rings have a number of fascinating properties: Ground-state persistent currents, strong Aharonov-Bohm interference effects, and an oscillatory dependence of the wavefunctions and all thermodynamic quantities on the enclosed magnetic flux, with period given by the flux quantum. This research will focus on the properties of individual and multiply-connected quantum rings in the few-electron and Coulomb blockade regime. The PI has recently discovered that inhomogeneous strain relaxation in sufficiently small Si/SiGe quantum dots leads to ring-like confinement. Additionally, tunneling measurements have confirmed the expected flux quantum periodicity. Given the control over device geometry, elliptical rings and coupled ring structures will be fabricated and few-carrier energy spectra, spin interactions, and Coulomb blockade effects will be measured as these rings are filled by carriers from zero carrier occupancy. The work will be coupled to state-of-the-art finite-element solid mechanics simulations. Experiment data will provide feedback on the interplay between electronic and mechanical properties in nanostructures. Graduate students involved in this research will acquire a full complement of skills, from deep-submicron fabrication, to low-temperature, low-signal measurements, to numerical simulation, which will prepare them for employment in academia, the semiconductor industry, or government. A teaching plan focusing on improved undergraduate teaching of core courses in the Electrical Engineering program is an integral part of this project. Ideal quantum rings, in which carriers follow circular orbits without scattering, have fascinating properties: Currents that flow without resistance, phase-interference effects, and the oscillatory dependence of carrier energies and wavefunctions on the enclosed magnetic flux. Quantum rings have also been suggested as possible building blocks for quantum computation. This research will focus on the properties of individual and multiply-connected quantum rings in the few-electron and Coulomb blockade regime, where the one carrier circling the ring affects the probability of another tunneling into the ring. The rings in question arise from the strain relaxation at the sidewalls of etched structures, making it possible to control the geometry (circular or elliptical) and the topology (single-ring or multiply-connected ring) of the system. Tunneling current measurements will study the carrier and spin interactions as these rings are filled by carriers from zero; the results will be compared to state-of-the-art finite-element strain simulations and our data will provide experimental feedback on the interplay between electronic and mechanical properties of nanostructures. Graduate students involved in this research will acquire a full complement of skills, preparing them for research jobs in academia, the semiconductor industry, or government. A teaching plan focusing on improved undergraduate teaching of core courses in the Electrical Engineering program is an integral part of the project.