Abstract Body

Superconducting vortex, as a manifestation of macroscopic quantum effects, is one of the central subjects in the physics of superconductivity. Diverse vortex phases such as vortex lattice and vortex liquid are fascinating subjects. In addition, non-trivial quantization, such as a half-quantum vortex, is proposed to emerge as a signature of unconventional pairing symmetry. Techniques that can quantitatively image quantum vortices under various temperatures, pressures, and magnetic fields would help explore various superconductivity with open questions.

Several techniques are known for local magnetic-field imaging of vortices [1,2]. Among them, the use of nitrogen-vacancy (NV) centers in diamonds as quantum sensors is recent [2]. Magnetic field imaging with a wide field of view broader than 100 µm×100 µm is possible with a camera and NV ensemble sensors. Such wide-field imaging is beneficial regarding high throughput and usages in extreme environments such as ultrahigh pressure. However, the inhomogeneity of the NV ensemble sensors has made it challenging to achieve accuracy comparable to a scanning technique with a conventional wide-field approach.

Here, we report a quantitative wide-field magnetic imaging of superconducting vortices in a typical high-Tc superconductor YBCO thin film [3]. A perfectly aligned NV ensemble sensor and analyses that include eliminating sensor inhomogeneities due to strain distribution accurately determine the magnetic field density. The result of the statistical analysis of the stray field distribution of a single vortex is consistent with the theoretical model and previous experimental results. It provides an alternative method for estimating the magnetic field penetration depth. Our technique, which combines high throughput and accuracy, is helpful for comprehensive characterization, including exploring unconventional superconductors.

References

[1] For example, J. R. Kirtley, Rep. Prog. Phys. 73, 126501 (2010); A. Finkler, et al. Rev. Sci. Inst. 83, 073702 (2012).
[2] For example, E. V. Levine et al. Nanophotonics 8, 1945 (2019); S. C. Scholten et al., J. Appl. Phys. 130, 150902 (2021); E. Marchiori et al., Nat. Rev. Phys. 4, 49 (2022).
[3] S. Nishimura et al. arXiv:2304.01024.

Acknowledgment

This work was carried out in collaboration with Shunsuke Nishimura, Kento Sasaki, Taku Kobayashi, and Daichi Sasaki (The University of Tokyo), and Takeyuki Tsuji, Takayuki Iwasaki, and Mutsuko Hatano (Tokyo Institute of Technology).