Scientific Reports 4: Article number: 7507; published online: 16 December 2014; updated: 25 February 2016.

This Article contains a typographical error in a grant number in the Acknowledgements section.

“This work was supported by the NSF of China (Grant Nos. 51332001, 11234005, 51472140 and 51221291), and the NSF (Grant No: DMR-1410714, DMR-0820404, and DMR-1210588).”

should read:

“This work was supported by the NSF of China (Grant Nos. 51332001, 11234005, 51472140 and 51221291), and the NSF (Grant No: DMR-1410714, DMR1420620, and DMR-1210588).”