1. Laboratoire
de Physique des Solides, Université Paris-Sud, CNRS, 91400 Orsay, France
2. Center
for Condensed Matter Theory, Department of Physics, Indian Institute of Science, Bangalore, Karnataka 560012, India
3. European Synchrotron Radiation Facility (ESRF), 6 rue Jules Horowitz, F-38043 Grenoble Cedex, France
4. Institute
for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, 1 avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France