L. J. Chang,1,2,* W. Schweika,3 Y. -J. Kao,4,5 Y. Z. Chou,4,6 J. Person,3 Th. Bruckel,3 H. C. Yang,4 Y. Y. Chen,7 and J. S. Gardner8 1Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan 2Quantum Beam Science Directorate, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan 3Institut fur Festkoerperforschung, Forschungszentrum Julich, DE-52425 Julich, Germany 4Department of Physics, National Taiwan University, Taipei 106, Taiwan 5Center of Quantum Science and Engineering, National Taiwan University, Taipei 10607, Taiwan 6Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA 7Institute of Physics, Academia Sinica, Nankang Taipei 115, Taiwan 8Indiana University, 2401 Milo B. Sampson Lane, Bloomington, Indiana 47408, USA (Received 1 November 2010; revised manuscript received 17 February 2011; published 18 April 2011)