[1] Wayne State Univ, Dept Phys & Astron, Detroit, MI 48201 USA
[2] Univ Illinois, Dept Phys, Urbana, IL 61801 USA
[3] Univ Illinois, Mat Res Lab, Urbana, IL 61801 USA
[4] Argonne Natl Lab, Div Mat Sci, Lemont, IL 60439 USA
[5] Yale Univ, Dept Phys, New Haven, CT 06520 USA
[6] Donostia Int Phys Ctr, P Manuel Lardizabal 4, San Sebastian 20018, Spain
[7] Max Planck Inst Chem Phys Solids, D-01187 Dresden, Germany
[8] Univ Illinois, Dept Mat Sci & Engn, Urbana, IL 61801 USA
[9] Univ Illinois, Dept Elect & Comp Engn, Urbana, IL 61801 USA
[10] Univ Illinois, Inst Condensed Matter Theory, Urbana, IL 61801 USA