Scientific Reports 5: Article number: 15796; published online: 29 October 2015; updated: 07 June 2017

In this Article, an affiliation has been omitted for Ya-Fen Hsu. The correct affiliations are listed below:

Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan.

Physics Division, National Center for Theoretical Science, Hsinchu, 30013, Taiwan.