Direct observation of Josephson vortex cores. - Roditchev, Dimitri; Brun, Christophe; Serrier-Garcia, Lise; Cuevas, Juan Carlos; Bessa, Vagner Henrique Loiola; Milošević, Milorad Vlado; Debontridder, François; Stolyarov, Vasily; Cren, Tristan (Nature Physics, 2015)