低温宽场氮空位显微镜中超导性的Laser调制
Laser modulation of superconductivity in a cryogenic widefield nitrogen-vacancy microscope
摘要：
基于金刚石中的氮空位（NV）中心的显微成像，越来越多地用于凝聚态系统的室温研究的工具，最近已扩展到低温条件。然而，它仍然不清楚该技术是否是可行的成像温度敏感的现象低于10 K给定的固有的激光照明的要求，特别是在宽场配置。在这里，我们实现了一个宽视场NV显微镜的视场为100 $μ$ m和4 K的基础温度，并使用它来成像Abrikosov涡旋和传输电流的超导Nb膜。我们观察到消失的漩涡时，激光功率的增加和减少时，他们的聚集热点，表明激光功率低至1毫瓦（4个数量级以下的NV饱和）是足够的局部淬火的超导电性的膜（$T_c = 9$ K）。这种显着的局部加热证实了电阻测量，这揭示了存在的大的温度梯度（几个K）的整个膜。然后，我们调查的影响，这样的梯度上的运输电流，其中的电流路径被认为是相关的温度分布，即使在完全超导相。除了突出温度不均匀性在超导现象中的作用外，这项工作还确定，在足够低的激光功率条件下，宽场NV显微镜可以在介观尺度下成像，分辨率可达4 K，为从拓扑绝缘体到范德华铁磁体的一系列系统的真实空间调查提供了一个新的平台。
英文摘要：
Microscopic imaging based on nitrogen-vacancy (NV) centres in diamond, a tool increasingly used for room-temperature studies of condensed matter systems, has recently been extended to cryogenic conditions. However, it remains unclear whether the technique is viable for imaging temperature-sensitive phenomena below 10 K given the inherent laser illumination requirements, especially in a widefield configuration. Here we realise a widefield NV microscope with a field of view of 100 $μ$m and a base temperature of 4 K, and use it to image Abrikosov vortices and transport currents in a superconducting Nb film. We observe the disappearance of vortices upon increase of laser power and their clustering about hot spots upon decrease, indicating that laser powers as low as 1 mW (4 orders of magnitude below the NV saturation) are sufficient to locally quench the superconductivity of the film ($T_c = 9$ K). This significant local heating is confirmed by resistance measurements, which reveal the presence of large temperature gradients (several K) across the film. We then investigate the effect of such gradients on transport currents, where the current path is seen to correlate with the temperature profile even in the fully superconducting phase. In addition to highlighting the role of temperature inhomogeneities in superconductivity phenomena, this work establishes that, under sufficiently low laser power conditions, widefield NV microscopy enables imaging over mesoscopic scales down to 4 K with a submicrometer spatial resolution, providing a new platform for real-space investigations of a range of systems from topological insulators to van der Waals ferromagnets.
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