高温超导体磁通钉扎和磁通动力学研究简介  

Brief introduction to flux pinning and vortex dynamics in high temperature superconductors

作　　者：闻海虎[1] Wen Hai-Hu(Physics Department,Nanjing University,Nanjing 210093,China)

机构地区：[1]南京大学物理学院,南京210093

出　　处：《物理学报》2021年第1期137-153,共17页Acta Physica Sinica

摘　　要：超导态是一个宏观量子相干态,其载流子是库珀对.在没有外加磁场和电流的时候,这些库珀对的运动行为用统一的波函数ψ=ψ0eiφ进行描述,其相位φ在宏观尺度上是相同的.当磁场低于一定值的时候,在超导体的边界处穿透深度内会出现一个屏蔽电流来对抗外磁场的侵入,样品处于迈斯纳态.然而,当磁场超过一定值的时候,磁场会进入到超导体中,迈斯纳态被破坏掉,在超导体内形成超导区和正常区及其相应的界面.根据此时这个界面处能量的正负,把超导体分成Ⅰ类和Ⅱ类超导体,分别对应正和负界面能.目前发现的绝大多数超导体都是Ⅱ类超导体,因为界面能为负值,因此进入到超导体的磁场会分离成最细小的单元,以保证最大的界面面积,降低系统能量.该最小的磁通束被称为磁通量子,其磁通量是Φ0=h/2e(h为普朗克常数, e为电子电量).这些磁通线之间有一定的排斥力,因此它们会形成点阵.当外加输运电流的时候,这些磁通线会受到一个洛伦兹力作用而运动,但是运动就会造成能量的损耗,超导体就会因此失去电阻为零的优良品质.通过在超导体中引入一些缺陷、杂质或位错,就可以把磁通钉扎住,超导体仍然可以有零损耗特性,而这个特性可以用于超导体的强电应用.本文将对磁通钉扎和磁通动力学及其研究方法做一点简单介绍.Superconductivity is achieved through macroscopic phase coherence;the charge carriers are Cooper pairs.In absence of an external magnetic field and applied current, the behavior of these Cooper pairs can bedescribed by a single wave function ψ=ψ0e^iφ, and the phase is uniform over the space. When applying anexternal field but still below a certain threshold, a screening current will be established at the surface, whichprohibits the entering of magnetic field, that is so-called Meissner effect. When the external field is larger thanthis threshold, the magnetic flux will penetrate into the sample, forming the interface of superconducting andnormal state regions. According to the sign of this interface energy, we can categorize superconductors intotype-Ⅰ (positive interface energy) and type-Ⅱ (negative interface energy). Most superconductors found so far aretype-Ⅱ in nature. Due to the negative interface energy in type-Ⅱ superconductors, the penetrated magnetic fluxwill separate into the smallest bundle, namely the quantum flux line, with a quantized flux Ф0=h/2e(h is thePlanck constant and e is the charge of an electron). There are weak repulsive interactions among these vortices,thus usually they will form a lattice, called mixed state. When applying a current, a Lorentz force will exert onthe flux lines (vortices) and will make them to move, this will induce energy dissipation and the appreciablefeature of zero resistance of a superconductor will be lost. By introducing some defects, impurities ordislocations into the system, it is possible to pin down these vortices and restore the state of zero resistance.The study concerning vortex pinning and dynamics is very important, which helps not only the understandingof fundamental physics, but also to the high power application of type-Ⅱ superconductors. This paper gives abrief introduction to the vortex dynamics of type-Ⅱ superconductors.

关 键 词：高温超导体 磁通动力学 铜氧化物超导体 铁基超导体 

分 类 号：TM26[一般工业技术—材料科学与工程]