[1] Univ Pavia, CNISM, I-27100 Pavia, Italy
[2] Univ Pavia, Dipartimento Fis A Volta, I-27100 Pavia, Italy
[3] Univ Florida, Dept Mat Sci & Engn, Gainesville, FL 32611 USA
[4] Oak Ridge Natl Lab, Oak Ridge, TN 37831 USA
[5] Acad Sci Czech Republ, Inst Phys, Prague 18221 8, Czech Republic
[6] RAS, AF Ioffe Physicotech Inst, St Petersburg 194021, Russia