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Abrikosov vortices hosting robust and well isolated zero-energy bound states have been recently found in FeTe$_{0.55}$Se$_{0.45}$, as reported by several different STM groups [1-3]. These vortices attract attention as the possible building blocks in a scenario of fault-tolerant quantum computing [4]. In this material, zero-energy bound states had been reported earlier in zero field close to Fe impurities [5] — where finite-energy states are expected instead — and remained unexplained, until it was proposed last year that a vortex spontaneously nucleates at the Fe impurity [6]. In this FLAT Club, I will present a spectacular recent experiment [arXiv:2001.07376], where this spontaneous vortex is switched on and off by using the STM tip to tune the exchange coupling with the impurity.


[1] Wang et al., Science 362, 333 (2018) [10.1126/science.aao1797]

[2] Machida et al., Nat. Mater. 18, 811 (2019) [10.1038/s41563-019-0397-1]

[3] Chen et al., arXiv:1909.01686 (2019)

[4] Ivanov, Phys. Rev. Lett. 86, 268 (2001) [10.1103/PhysRevLett.86.268]

[5] Yin et al., Nat. Phys. 11, 543 (2015) [10.1038/NPHYS3371]

[6] Jiang et al., Phys. Rev. X 9, 011033 (2019) [10.1103/PhysRevX.9.011033]