1. Institute
for Solid State Physics, University of Latvia, Kengaraga 8, LV-1063 Riga, Latvia
2. Forschungszentrum Jülich, Institute of Energy and Climate
Research, IEK-1, Materials Synthesis and Processing, 52425 Jülich, Germany
3. Max Planck Institute for Solid State Research, Heisenbergstr. 1, D-70569 Stuttgart, Germany