About the Authors

Petter Holme

petter.holme@physics.umu.se

Affiliations Department of Physics, Umeå University, Umeå, Sweden, Department of Energy Science, Sungkyunkwan University, Suwon, Republic of Korea

Competing Interests

The author has declared that no competing interests exist.

Author Contributions

Conceived and designed the experiments: PH. Performed the experiments: PH. Analyzed the data: PH. Contributed reagents/materials/analysis tools: PH. Wrote the paper: PH.