The Au POSCs were prepared by the controlled-atmosphere flame fusion (CAFF) approach. A detailed description of the procedure, as well as the individual components of the single crystal growth setup, can be found in Refs. 49 and 48. The most important com-ponents and experimental steps for preparation are summarized in the following. The Au POSCs were prepared from a Au wire, which was first melted in a H 2 , O 2 , Ar flame (0.7 H 2 (purity: 5.0, Westfalen AG), 0.1 O 2 (purity: 3.5 MTI IndustrieGase AG), 1.0 Ar (flame) (4.6, MTI IndustrieGase AG)) so that a Au bead was formed at the lower end of the Au wire. Once the bead had the desired size, the molten Au bead was slowly cooled at a defined rate, by pulling the bead out of the flame, resulting in the formation of a POSC. Impurities from the wire, which accumulated at the top of the bead during cooling, were removed by etching in aqua regia for about 30 min after the bead had cooled completely. Subsequently, the bead was re-melted and cooled following the same procedure as starting from a Au wire. When the bead restructured during the experiments described in this manuscript, a fresh bead was prepared according to the same procedure described above.