About the Authors

Jan Opfer
Kay-Eberhard Gottschalk


Affiliation Institut für Experimentelle Physik, Universität Ulm, Ulm, Germany

Competing Interests

The authors have declared that no competing interests exist.

Author Contributions

Conceived and designed the experiments: JO KEG. Performed the experiments: JO. Analyzed the data: JO KEG. Wrote the paper: JO KEG.