Nature Physics 6, 584–588 (2010); published online 13 June 2010; corrected after print 12 August 2010.

On the first page of the PDF and printed versions of this Letter originally published, the full list of authors and their affiliations (shown below) should have been included. This has been corrected on the PDF version of the Letter.

Yi Zhang1, Ke He1*, Cui-Zu Chang1,2, Can-Li Song1,2, Li-Li Wang1, Xi Chen2, Jin-Feng Jia2, Zhong Fang1, Xi Dai1, Wen-Yu Shan3, Shun-Qing Shen3, Qian Niu4, Xiao-Liang Qi5, Shou-Cheng Zhang5, Xu-Cun Ma1 and Qi-Kun Xue1,2*

1Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China, 2Department of Physics, Tsinghua University, Beijing 100084, China, 3Department of Physics and Center for Theoretical and Computational Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China, 4Department of Physics, The University of Texas, Austin, Texas 78712-0264, USA, 5Department of Physics, Stanford University, Stanford, California 94305-4045, USA. *e-mail: kehe@aphy.iphy.ac.cn; qkxue@mail.tsinghua.edu.cn.