Christophe Berthod, Ivan Maggio-Aprile, Jens Bruér, Andreas Erb, Christoph Renner: Observation of Caroli--de Gennes--Matricon Vortex States in $\mathrmYBa_2\mathrmCu_3\mathrmO_7\ensuremath-\ensuremath\delta$. American Physical Society 2017Phys. Rev. Lett.: 119. https://link.aps.org/doi/10.1103/PhysRevLett.119.237001