1. Department
of Materials and Environmental Chemistry, Stockholm University, SE-106
91 Stockholm, Sweden
2. Institute
for Physics of Condensed Matter, TU Braunschweig, D-38106 Braunschweig, Germany
3. B. I. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, Kharkov 61103, Ukraine
4. Department
of Chemistry and Texas Center for Superconductivity, University of Houston, 112 Fleming Building, Houston, Texas 77204-5003, United States