[1] Univ Politecn Cataluna, Dept Fis, EEBE, Campus Diagonal Besos,Eduard Maristany 10-14, Barcelona 08019, Catalonia, Spain
[2] Univ Politecn Cataluna, Barcelona Res Ctr Multiscale Sci & Engn, Eduard Maristany 10-14, Barcelona 08019, Catalonia, Spain
[3] Univ Barcelona, Fac Fis, Dept Fis Mat Condensada, Marti & Franques 1, E-08028 Barcelona, Catalonia, Spain
[4] Los Alamos Natl Lab, Div Theoret, Los Alamos, NM 87545 USA