介观超导体中的电磁响应

Due to the quantum and boundary effects caused by finite size confinement, mesoscopic superconductors can have different electromagnetic response from the bulk materials, which is important to detect microscopic mechanisms of different superconductors and to realize electromagnetic control in small size superconducting devices. Particularly in recent years, as a result of the fast development of the sample growth and measurement techniques together with some anomalous experimental results, the electromagnetic response in mesoscopic superconductors becomes an urgent theoretical question. We plan to study the superconductivity and electromagnetic response self-consistently from different perspectives including mesoscopic quantum effect, surface boundary state, superconducting proximity effect, electron correlation, disorder, retarded pairing mechanism and so on, in order to reveal their different electromagnetic properties from the macroscopic systems. We aim to solve or partially solve several important scientific problems: (1) anomalous behaviors of the superfluid density in overdoped cuprate films; (2) electromagnetic control in superconducting field effect transistors; (3) the interplay between electromagnetic fields and superconducting heterostructures. Our study will provide theoretical support for future theoretical and experimental researches and potential applications of mesoscopic superconducting devices.

由于尺寸受限所带来的量子效应和边界效应，介观超导体会表现出与体超导材料不同的电磁响应。这对于探究不同超导体的微观机理以及实现小尺寸超导器件的电磁调控具有重要意义。尤其是近些年来，实验上样品制备与测量技术的快速发展以及一些反常实验现象的相继发现，使得介观超导体中的电磁响应成为一个亟待解决的理论问题。本项目拟从多个角度，包括介观量子效应、表面束缚态、超导近邻效应、电子关联效应、无序以及配对的推迟效应等，自洽的探究其对超导序参量以及电磁场的影响，从而揭示出其与宏观系统不同的电磁性质。本项目拟重点解决或部分解决几个重要的科学问题：（1）过掺铜氧超导薄膜中超流密度的反常行为；（2）超导场效应管中的电磁调控；（3）电磁场与超导异质结的相互影响等，从而为进一步的理论实验研究和介观超导器件的潜在应用提供理论支持。

本项目从非常规超导体（包括介观样品）中的一些反常电磁响应等实验结果出发，研究了过掺铜氧超导体、Sr2RuO4、反常同位素效应、超导二极管效应等。同时伴随着量子多体技术的发展和转角体系的实验理论进展，我们也对相关的量子多体模型进行了一系列研究。取得的主要研究成果如下：（1）我们成功的利用杂质效应解释了过掺铜氧超导体中的一些反常实验结果，包括超流密度、光电导、霍尔效应、磁阻等，也对Sr2RuO4中单轴压实验与多分量配对之间的矛盾进行了调和。（2）对于反常同位素效应，我们利用双玻色模的BCS理论提供了一种最为简单的解释。（3）在转角多层石墨烯中，发现双量子临界点的行为并可以被磁场调控。（4）阐述了超导二极管效应中的对称性原则。（5）对相关的一些量子多体模型通过不同的手段进行求解，丰富并完善了我们对于强关联体系的认识。