Artificial Atoms

提出了实验来探索电子被限制在一个小区域的空间和耦合到附近的金属引线的物理。要研究的特定系统是单电子晶体管（SET）。在过去几年中进行的实验已经揭示了约束电子液滴和引线之间的强耦合效应。特别是，他们已经证明了安德森哈密顿量，连同标度和重整化理论，提供了平衡（零偏置）电导作为温度和栅极电压函数的定量描述。具体来说，耦合系统的基态是近藤单重态。这些结果的发表刺激了许多理论预测，而拟议研究的一个目标是验证这些预测。差分电导作为偏置的函数将被研究。此外，还将研究多个水平对近藤效应的影响。在磁场中，与近藤单线态有关的微分电导峰值分裂为两部分。已经对这些峰的分裂进行了预测，并将测试它们的线形随磁场的演变。一个新的测量设备已经建成，它将允许近藤效应的测量扩展到更低的温度。该系统配有16T磁铁和旋转台，使磁场可处于或垂直于电子液滴的平面。这将允许测量的温度依赖的近藤峰在差分电导精确。最近在set中发现了一种完全不同的现象，即范诺干扰。对于小的set，单电子线的形状与Fano理论预测的特征形状是不对称的。后者需要一个连续的传输通道来干扰谐振通道。计划进行实验以阐明这种干扰的性质。特别是，共振通道似乎是由单电子添加产生的，而连续通道的起源是一个谜。测量温度和磁场对线形的依赖性可以澄清微观物理。这项研究将与学生一起完成，他们将因此接受纳米科学和技术前沿领域的培训。二十世纪下半叶最引人注目的现象是由半导体技术成本的降低和效率的提高所推动的技术革命。我们经常用“摩尔定律”来描述这一点，即硅芯片上晶体管数量的指数增长。40多年来，后一个数字每18个月就以2倍的速度增长。这次爆炸是由于基础半导体物理学的发现而成为可能的。然而，为了维持它，科学家和工程师需要新的技术来制造越来越小的结构，所以现在有可能制造只有纳米大小的半导体结构。传统晶体管中的电子表现得像经典粒子，而局限于小维度的电子只能用量子力学来描述。因此，物理学上的发现带来了新技术，这使我们现在有可能研究新的物理学。这项研究将探索限于纳米尺度的电子物理学。这种结构被称为单电子晶体管（SET）。晶体管是一种开关，当电子加入时它就打开，当电子被移除时它就关闭。例如，今天在蜂窝电话或个人电脑中使用的传统晶体管需要大约1000个电子才能打开。SET每次添加一个电子晶体管时，它就会再次打开和关闭。这项研究的目标是了解电子是如何在晶体管的陷阱和电极之间分布的，以及这种分布是如何依赖于SET的特性、温度和外加磁场的。对于各种纳米电子结构，其物理性质是相似的，因此将在纳米科学和纳米技术中有广泛的应用。研究生和本科生将参与本研究。他们将接受纳米科学和纳米技术前沿领域之一的培训，这将为他们在学术界、工业界和政府机构的就业做好准备。* * *

Experiments are proposed to explore the physics of electrons confined to a small region of space and coupled to nearby metallic leads. The particular system to be studied is the single-electron transistor (SET). Experiments carried out in the past few years have revealed the effects of strong coupling between the confined electron droplet and the leads in an SET. In particular, they have demonstrated that the Anderson Hamiltonian, together with scaling and renormalization theories, provides a quantitative description of the equilibrium (zero-bias) conductance as a function of temperature and gate voltage. Specifically, the ground state of the coupled system is a Kondo singlet. The publication of these results has stimulated a number of theoretical predictions, and one goal of the proposed research is to test these predictions. The differential conductance as a function of bias will be studied. In addition, the effects of multiple levels on the Kondo effect will be examined. In a magnetic field the peak in differential conductance associated with the Kondo singlet splits in two. Predictions have been made of the splitting of these peaks and the evolution of their line shape with magnetic field will be tested. A new measurement facility has been constructed which will allow the measurement of the Kondo effect to be extended to lower temperature. The system is equipped with a 16T magnet and rotation stage, so that the field can be in the plane or perpendicular to the plane of the droplet of electrons. This will allow the measurement of the temperature dependence of the Kondo peak in differential conductance precisely. A completely different phenomenon, recently discovered in SETs, is Fano interference. For small SETs the single-electron line shapes are asymmetric with the characteristic shape predicted by the Fano theory. The latter requires a continuous transmission channel that interferes with a resonant one. Experiments are planned to clarify the nature of this interference. In particular, while the resonant channel appears to arise from single electron addition, the origin of the continuous channel is a mystery. Measurement of the temperature and magnetic field dependence of the line shapes may clarify the microscopic physics. This research will be done with students who will thereby receive training in a cutting edge area of nanoscience and technology. %%%The most dramatic phenomenon of the last half of the twentieth century is the technological revolution, driven by the decrease in cost and increase in efficiency of semiconductor technology. We often describe this by "Moore's Law", the exponential increase in the number of transistors on a silicon chip. The latter number has been increasing by a factor two every eighteen months for over forty years. This explosion was made possible by discoveries in fundamental semiconductor physics. However, in order to sustain it, scientists and engineers needed new technologies for making smaller and smaller structures, so that it is now possible to make semiconductor structures that are only nanometers in size. Whereas electrons in conventional transistors behave like classical particles, electrons confined to small dimensions can only be described by quantum mechanics. Thus, discoveries in physics led to new technology, which now make it possible for us to study new physics. This research will explore the physics of electrons confined to nanometer dimensions. The structure focused on is called a single electron transistor (SET). A transistor is a switch that turns on when electrons are added to it and turns off when they are removed. The conventional transistor of today, in a cellular telephone or personal computer, for example, requires about 1000 electrons to turn on. The SET turns on and off again every time a single electron transistor is added to it. The goal of this research is to understand how the electron is distributed between the trap and the electrodes of the transistor and how this distribution depends on the properties of the SET, the temperature and an applied magnetic field. The physics is expected to be similar for a wide variety of nano-electronic structures and so will be of broad application to nanoscience and nanotechnology. Graduate and undergraduate students will participate in this research. They will receive training in one of the forefront areas of nanoscience and nanotechnology that will prepare them for employment in academe, industry and government institutions. ***