Experimental Study of Superconductor/Ferromagnet Proximity Effects

非技术摘要：许多有用的电子设备都是由铁磁性薄膜制成的，例如计算机硬盘驱动器的读头和写头。有用的设备也是由超导薄膜制成的，包括从心跳和大脑活动中检测磁场的医疗系统。最近在制造和测量薄膜结构的实验设备的尖端和理论上的进步，为可能的将超导和铁磁薄膜近距离结合的装置开辟了一条新的途径。科学中真正令人兴奋的方面，以及新设备功能的一个重要机制，来自于当两种材料处于如此密切的接触时，铁磁体内部的超导持久性，使得电子可以从超导体自由扩散到铁磁体，然后再扩散回来。该项目将通过大型和纳米设备中的磁场屏蔽测量直接研究铁磁体中的超导电子，并间接通过电子隧道测量来研究。该项目将涉及研究生和本科生制造SC/FM器件以及复杂的测量。技术摘要：超导和铁磁性是对立的，前者要求电子形成自旋零对，而后者要求平行电子自旋。最近，人们已经意识到，样品制造和测量技术已经变得足够复杂，以至于可以重复地创建和研究与铁磁体密切接触的超导体的相互作用。理论的一个令人惊讶的结果是，超导电性可以持续存在于铁磁体中。该项目将探索不同SC/FM双层和三层结构的FM层中与超流相关的有效超流密度。超流密度将通过磁屏蔽测量直接测量，包括SC/FM双层或三层相反侧线圈的互感，以及通过纳米级图案导线的传输测量，以了解降维的影响。它还将通过隧道测量到承载着超级电流的SC/FM双层的FM薄膜中进行研究。该项目将让研究生和本科生参与SC/FM器件的制造以及复杂的测量。

Non-technical Abstract:Many useful electronic devices are made from ferromagnetic films, such as read and write heads for computer hard drives. Useful devices are made from superconducting films, too, including medical systems that detect magnetic fields from heartbeats and brain activity. Recent advances in the sophistication of experimental apparatus for making thin-film structures and for measuring them, and advances in theory, have opened a new avenue for possible devices that incorporate superconducting and ferromagnetic films in close proximity. The really exciting aspect of the science, and an important mechanism for new device functionalities, comes from the persistence of superconductivity inside the ferromagnet when the two materials are in such intimate contact such that electrons can diffuse freely from superconductor to ferromagnet and back. This project will study superconducting electrons in the ferromagnet directly via magnetic field screening measurements in large and nano-scale devices, and indirectly via electron tunneling measurements. The project will involve graduate and undergraduate students in fabrication of SC/FM devices as well as sophisticated measurements.Technical Abstract:Superconductivity and ferromagnetism are antithetical, the former demanding that electrons form spin-zero pairs and the latter pressing for parallel electron spins. Recently it has been appreciated that sample fabrication and measurement techniques have become sufficiently sophisticated that the mutual interactions of superconductors in intimate contact with ferromagnets can be reproducibly created and studied. A surprising result of theory is that superconductivity can persist into the ferromagnet. This project will explore the effective superfluid density associated with supercurrents in the FM layer of various SC/FM bilayer and trilayer structures. The superfluid density will be measured directly via magnetic screening measurements involving the mutual inductance of coils on opposite sides of a SC/FM bilayer or trilayer, and via transport measurements on nanoscale patterned wires, to see the effects of reduced dimensionality. It will also be studied via tunneling measurements into the FM film of a SC/FM bilayer that is carrying a supercurrent. The project will involve graduate and undergraduate students in fabrication of SC/FM devices as well as sophisticated measurements.