Quantum Coherent Phenomena in Superconducting Heterostructures

* 非技术性摘要 * 根据量子力学，像电子这样的小物体除了表现得像离散粒子之外，还表现得像波。 作为波，电子表现出许多有趣的效应。 波的干涉就是一个例子：想象一下当一个小池塘里扔了一块石头时，水面上的波的模式。量子波也编码了粒子之间各种相互作用和相关性的结果，利用这些效应的设备是许多现代电子设备的基本组成部分。 由于电子的波动性质，电子之间的干扰和相关性的影响可以通过测量它们产生的电流来观察。 然而，这些脆弱的干扰和相关效应很容易被破坏，并且需要极低的温度（接近绝对零度）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，这些电子是由它们与超导体的相互作用引起的，超导体是一种可以在非常低的温度下无电阻地传输电流的材料。 将使用的实验技术包括制造非常小的设备，包括金属和超导部件，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，他们将学习纳米纤维和设备测量的复杂技术。 这项培训将使学生有在学术界或高科技行业的职业生涯。*技术摘要 * 本项目将探索由于与超导体的相互作用而在正常金属和铁磁体中诱导的量子关联。 特别是，该项目的主要重点将是在空间分离的正常金属和铁磁体中引入的非局部相关性，这些相关性由交叉Andreev反射（CAR）和弹性共隧穿（EC）引起。 CAR和EC将使用非本地电传输测量以及噪声测量进行探测。 噪声测量也将用于探测自旋纠缠的准粒子使用样品与铁磁元素。 第二组测量将集中在条件下，人们可以观察到超导相关性在长尺度的系统与有限的自旋极化。 虽然在铁磁体中观察到了超导相关性，但这些相关性延伸的长度尺度非常短。 将被研究的新材料系统可能会扩展这种长度范围，并导致新的超导设备的可能性，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。 该项目的组成部分是对研究生和本科生进行纳米纤维和复杂测量技术的培训。

****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.