Experimental Study of Superconductor/Ferromagnet Proximity Effects

摘要：许多有用的电子设备都是由铁磁薄膜制成的，例如计算机硬盘驱动器的读写头。有用的设备也由超导薄膜制成，包括从心跳和大脑活动中检测磁场的医疗系统。制造薄膜结构和测量薄膜结构的实验装置的最新进展，以及理论的进步，为将超导和铁磁薄膜紧密结合在一起的可能装置开辟了一条新的途径。这门科学真正令人兴奋的方面，以及新设备功能的重要机制，来自铁磁体内部超导性的持续存在，当两种材料紧密接触时，电子可以自由地从超导体扩散到铁磁体，然后再扩散回来。该项目将通过在大型和纳米级设备上的磁场筛选测量直接研究铁磁体中的超导电子，并通过电子隧道测量间接研究。该项目将涉及研究生和本科生制造SC/FM设备以及复杂的测量。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，后者要求电子形成平行自旋。最近，人们认识到，样品制造和测量技术已经变得足够复杂，超导体与铁磁体密切接触的相互作用可以重复地创造和研究。一个令人惊讶的理论结果是，超导性可以持续到铁磁体中。本项目将探讨各种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。超流体密度将直接通过磁筛选测量来测量，包括SC/FM双层或三层两侧线圈的互感，以及通过纳米尺度图案导线的传输测量来观察降维的影响。它还将通过隧道测量进入携带超电流的SC/FM双层的FM膜来研究。该项目将涉及研究生和本科生制造SC/FM设备以及复杂的测量。

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.