用金刚石NV心光学磁强计研究超导体中的迈斯纳效应
Spatially - resolved study of the Meissner effect in superconductors using NV-centers-in-diamond optical magnetometry
摘要：
利用金刚石中氮空位（NV）中心的光探测磁共振非侵入式磁场传感技术，研究了几种典型超导体中弱磁场穿透和排出时磁感应强度的空间分布。用变温共焦系统测量了常规超导体Pb和Nb，非常规超导体LuNi $_2$ B $_2$ C，Ba $_{0.6}$ K $_{0.4}$ Fe $_2$ As $_2$，Ba（Fe $_{0.93}$ Co $_{0.07}$）$_2$ As $_2$，CaKFe $_4$ As $_4$表面的矢量磁场，具有衍射极限空间分辨率.在零场冷却（ZFC）和场冷却（FC）条件下测量了晶体边缘的磁感应强度分布。虽然所有超导体在冷却到远低于超导转变$T_c$的温度后都显示出几乎完美的磁场屏蔽，但在$T_c$上方的静磁场中冷却时，观察到迈斯纳驱逐的一系列非常不同的行为。在LuNi $_2$ B $_2$ C中发现了大量的常规迈斯纳驱逐，在Nb中发现了顺磁迈斯纳效应（PME），并且在铁基超导体中几乎没有观察到驱逐。在所有的情况下，与宏观测量的总磁矩的良好的相关性被发现。我们的空间分布的磁感应强度的测量提供洞察微观物理的迈斯纳效应。
英文摘要：
Non-invasive magnetic field sensing using optically - detected magnetic resonance of nitrogen-vacancy (NV) centers in diamond was used to study spatial distribution of the magnetic induction upon penetration and expulsion of weak magnetic fields in several representative superconductors. Vector magnetic fields were measured on the surface of conventional, Pb and Nb, and unconventional, LuNi$_2$B$_2$C, Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$, Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$, and CaKFe$_4$As$_4$, superconductors, with diffraction - limited spatial resolution using variable - temperature confocal system. Magnetic induction profiles across the crystal edges were measured in zero-field-cooled (ZFC) and field-cooled (FC) conditions. While all superconductors show nearly perfect screening of magnetic fields applied after cooling to temperatures well below the superconducting transition, $T_c$, a range of very different behaviors was observed for Meissner expulsion upon cooling in static magnetic field from above $T_c$. Substantial conventional Meissner expulsion is found in LuNi$_2$B$_2$C, paramagnetic Meissner effect (PME) is found in Nb, and virtually no expulsion is observed in iron-based superconductors. In all cases, good correlation with macroscopic measurements of total magnetic moment is found. Our measurements of the spatial distribution of magnetic induction provide insight into microscopic physics of the Meissner effect.
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