Quantum Coherent Phenomena in Superconducting Heterostructures

超导异质结构中的量子相干现象

• 批准号: 1006445
• 负责人: Venkat Chandrasekhar
• 金额: $ 48万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1006445&HistoricalAwards=false
• 关键词: Quantum; Coherent; Phenomena; Superconducting; Heterostructures

****NON-TECHNICAL ABSTRACT****According to quantum mechanics, small objects such as electrons behave like waves in addition to behaving like discrete particles. As waves, electrons show many interesting effects. An example is the interference of waves: think of the patterns of waves on the surface of a small pond when a stone is thrown in it. Quantum waves also encode the results of various interactions and correlations between particles, and devices that take advantage of these effects are the fundamental building blocks of many modern electronic devices. The effects of interference and correlations between electrons due to their wave nature can be seen by measuring the electric currents that are generated by them. However, these fragile interference and correlation effects are easily destroyed, and extremely low temperatures (close to absolute zero) and very sensitive measurement techniques are required to observe them. This project will explore correlations between electrons in metals that are induced by their interactions with a superconductor, which is a material that can carry an electrical current without resistance at very low temperatures. The experimental techniques that will be used include fabrication of very small devices that include metallic and superconducting parts, and measurements of the currents and voltages through these devices, as well as the electrical noise generated by these currents and voltages at very low temperatures. A major component of this project is the involvement of undergraduate and graduate students in research, who will learn sophisticated techniques of nanofabrication and device measurements. This training will enable the students to have careers in academia or high-technology industries.****TECHNICAL ABSTRACT****This project will explore quantum correlations induced in normal metals and ferromagnets due to their interactions with superconductors. In particular, the primary focus of this project will be on non-local correlations introduced in spatially separated normal metals and ferromagnets induced by crossed Andreev reflection (CAR) and elastic co-tunneling (EC). CAR and EC will be probed using nonlocal electrical transport measurements as well as noise measurements. The noise measurements will also be used to probe for spin entanglement of quasiparticles using samples with ferromagnetic elements. A second set of measurements will focus on the conditions under which one can observe superconducting correlations over long length scales in systems with finite spin polarization. While superconducting correlations have been observed in ferromagnets, the length scale over which these correlations extend has been extremely short. The new material systems that will be investigated may extend this length scale, and lead to the possibility of new superconducting devices in addition to furthering our understanding of exotic forms of superconductivity in ferromagnets. Integral to the project is the training of graduate and undergraduate students in nanofabrication and sophisticated measurement techniques.

****非技术摘要****根据量子力学，电子等小物体除了表现得像离散粒子外，还表现得像波。 作为波，电子表现出许多有趣的效应。 一个例子是波浪的干扰：想象一下当向一个小池塘扔一块石头时，它的表面会出现什么样的波浪图案。 量子波还对粒子之间各种相互作用和相关性的结果进行编码，而利用这些效应的设备是许多现代电子设备的基本构建模块。 通过测量电子产生的电流，可以看出电子之间由于其波动性而产生的干扰和相关性的影响。 然而，这些脆弱的干扰和相关效应很容易被破坏，需要极低的温度（接近绝对零）和非常灵敏的测量技术来观察它们。 该项目将探索金属中电子之间的相关性，这些电子是由金属与超导体相互作用而引起的，超导体是一种可以在极低温度下无电阻地承载电流的材料。 将使用的实验技术包括制造包含金属和超导部件的非常小的设备，并测量通过这些设备的电流和电压，以及这些电流和电压在非常低的温度下产生的电噪声。 该项目的一个主要组成部分是本科生和研究生参与研究，他们将学习纳米制造和设备测量的复杂技术。 这项培训将使学生能够在学术界或高科技行业从事职业。****技术摘要****该项目将探索普通金属和铁磁体由于与超导体相互作用而引起的量子相关性。 特别是，该项目的主要重点将是由交叉安德烈夫反射（CAR）和弹性共隧道（EC）引起的空间分离的普通金属和铁磁体中引入的非局部相关性。 将使用非局部电传输测量以及噪声测量来探测 CAR 和 EC。 噪声测量还将用于使用具有铁磁元素的样品来探测准粒子的自旋纠缠。 第二组测量将重点关注在有限自旋极化系统中可以在长尺度上观察超导相关性的条件。 虽然在铁磁体中观察到超导相关性，但这些相关性延伸的长度尺度非常短。 将要研究的新材料系统可能会扩展这个长度尺度，除了进一步加深我们对铁磁体中超导性的奇异形式的理解之外，还会带来新的超导器件的可能性。 该项目的一个组成部分是对研究生和本科生进行纳米制造和复杂测量技术方面的培训。