[1] Univ Calif San Diego, Dept Phys, La Jolla, CA 92093 USA
[2] Univ Calif San Diego, Inst Pure & Appl Phys Sci, La Jolla, CA 92093 USA
[3] Oak Ridge Natl Lab, Mat Sci & Technol Div, Oak Ridge, TN 37831 USA
[4] Lawrence Livermore Natl Lab, Livermore, CA 94551 USA
[5] Univ Alabama Birmingham, Dept Phys, Birmingham, AL 35294 USA