Experimental Studies of Persistent Currents in Normal Metals

****技术摘要****持续电流是介观物理中最引人注目的现象之一。无耗散电流流过电阻器的概念是相当违反直觉的，尽管在最简单的情况下，它是允许孤立原子在其电子基态中具有轨道角动量的相同现象的一种表现。在介观固体器件中，相当多的理论工作表明，持续电流可能对多种体效应相当敏感。然而，直到最近，持续电流的可靠测量在技术上是非常具有挑战性的。该项目将使用新开发的检测技术来测量预计许多身体效应占主导地位的地区的持续电流。具体来说，微机械扭转磁强计将用于测量低磁场下扩散金属环中的平均电流，其中已经预测到导致BCS超导的相同相互作用效应可以导致正常状态下显着增强的持续电流。此外，同样的技术将被用于测量高迁移率二维电子气体中的持续电流，无论是在低磁场下（持续电流可用于研究混沌或可积样品的光谱），还是在高磁场下，持续电流可用于探测准粒子的统计。该项目将支持培养一名博士生，该博士生将学习各种技术技能，包括半导体微纳米制造、低温学、光纤、微力学和超灵敏测量技术。****非技术摘要****将量子力学理论应用于整个电路的最引人注目的结果之一是预测，尽管电路有电阻，电流可以永远流过它而不获得或损失能量。这种现象被称为持续电流，它直接类似于我们更熟悉的原子核周围的电子轨道。然而，在电路的设置中，产生持续电流的轨道流经比单个原子长一万倍的金属导线。直到最近，人们还认为几乎不可能可靠地测量这些电流，但这个项目将使用新开发的测量技术来研究各种不同材料中的持续电流。这个目标的动机是一个理论预测，即持久电流的基本特性（例如，它的大小和流动方向）可以告诉我们很多关于两个奇异但极其重要的现象：超导（金属失去对电流的所有电阻）和分数量子霍尔态（半导体中的电子与磁场结合在一起，产生自然界中没有类似物的粒子）。这个项目将促进我们对这些现象的理解，也将产生用于研究小的、孤立的样品中的电子行为的新型仪器。该项目将支持培养一名博士生，该博士生将学习各种技术技能，包括半导体微纳米制造、低温学、光纤、微力学和超灵敏测量技术。

****TECHNICAL ABSTRACT****Persistent currents are one of the most dramatic phenomena of mesoscopic physics. The notion of a disipationless electrical current flowing through a resistor is quite counterintuitive, although at its simplest, it is a manifestation of the same phenomena that allows isolated atoms to posses orbital angular momentum in their electronic ground state. In mesoscopic solid-state devices, a considerable body of theoretical work suggests that persistent currents may be quite sensitive to a variety of many body effects. However until recently, the reliable measurement of persistent currents was technically very challenging. This project will use newly developed detection techniques to measure persistent currents in regimes where many body effects are expected to be dominant. Specifically, micromechanical torsional magnetometry will be used to measure the average current in diffusive metal rings at low magnetic fields, where it has been predicted that the same interaction effects that give rise to BCS superconductivity can lead to dramatically enhanced persistent current in the normal state. In addition, the same techniques will be used to measure the persistent current in high-mobility two dimensional electron gases, both in low magnetic fields (where the persistent current can be used to study the spectra of chaotic or integrable samples), and at high magnetic fields, where the persistent current can be used to probe the statistics of the quasiparticles. This project will support the training of a Ph.D. student, who will learn a variety of technical skills, including semiconductor micro- and nano-fabrication, cryogenics, fiber optics, micromechanics, and ultrasensitive measurement techniques.****NON-TECHNICAL ABSTRACT****One of the most striking results of applying the theory of quantum mechanics to an entire electrical circuit is the prediction that, despite the electrical resistance of the circuit, electrical current can flow perpetually through it without gaining or losing energy. This phenomenon is known as persistent current, and is directly analogous to the more familiar orbits of electrons around the nucleus of an atom. However in the setting of an electrical circuit, the orbitals which produce the persistent current are flowing through metal wires which are ten thousand times longer than a single atom. Until recently it was considered nearly impossible to measure these currents reliably, but this project will use newly-developed measurement techniques to study persistent currents in a variety of different materials. This goal is motivated by the theoretical prediction that the basic properties of the persistent current (for example, its size and the direction of its flow) can tell us a great deal about two exotic but extremely important phenomena: superconductivity (in which a metal loses all resistance to electrical currents) and the fractional quantum Hall state (in which electrons in a semiconductor bind together with a magnetic field to create particles that have no analog in nature). This project will advance our understanding of these phenomena, and will also result in new types of instruments for studying the behavior of electrons in small, isolated samples. This project will support the training of a Ph.D. student, who will learn a variety of technical skills, including semiconductor micro- and nano-fabrication, cryogenics, fiber optics, micromechanics, and ultrasensitive measurement techniques.