Non-quantized penetration of magnetic field in the vortex state of superconductors
Non-quantized penetration of magnetic field in the vortex state of superconductors
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DOI：
10.1038/35024025
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发表时间：
2000-09
期刊：
影响因子：
64.8
通讯作者：
A. Geim;A. Geim;S. Dubonos;I. Grigorieva;I. Grigorieva;K. Novoselov;F. M. Peeters;V. Schweigert-V.-Schwei
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文献类型：
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作者：
A. Geim;A. Geim;S. Dubonos;I. Grigorieva;I. Grigorieva;K. Novoselov;F. M. Peeters;V. Schweigert-V.-Schwei
正如Bardeen和Ginzburg在60年代初首次指出的那样，超导材料中涡旋携带的磁通量取决于它们到样品边缘的距离，并且可以小于一个磁通量，φ0=h/2e(他的普朗克常数是电荷)。在块状超导体中，这种磁通的减少在距离边缘亚微米的距离内变得可以忽略不计，但在薄膜中，这种效应可能会在材料中更远的地方存在。但这种影响还没有在实验上观察到，人们经常假设磁场以φ0为单位进入第二类超导体。在这里，我们测量了超导薄膜中单个涡旋引入的通量，发现通量总是与φ0有很大不同。我们观测到了低至0.001φ0的涡旋，以及“负涡”，它的穿透导致磁场的排出。我们区分了导致非量子化磁通穿透的两种现象：有限尺寸效应，和由于表面势垒的存在而产生的磁场的非线性屏蔽。后一种效应以前没有考虑过，但在大多数情况下可能会导致非量子化的穿透。
As first pointed out by Bardeen and Ginzburg in the early sixties,, the amount of magnetic flux carried by vortices in superconducting materials depends on their distance from the sample edge, and can be smaller than one flux quantum, φ0=h/2e(wherehis Planck's constant andeis the electronic charge). In bulk superconductors, this reduction of flux becomes negligible at sub-micrometre distances from the edge, but in thin films the effect may survive much farther into the material,. But the effect has not been observed experimentally, and it is often assumed that magnetic field enters type II superconductors in units of φ0. Here we measure the amount of flux introduced by individual vortices in a superconducting film, finding that the flux always differs substantially from φ0. We have observed vortices that carry as little as 0.001φ0, as well as ‘negative vortices’, whose penetration leads to the expulsion of magnetic field. We distinguish two phenomena responsible for non-quantized flux penetration: the finite-size effect,,,and a nonlinear screening of the magnetic field due to the presence of a surface barrier. The latter effect has not been considered previously, but is likely to cause non-quantized penetration in most cases.