1. Univ Lyon UJM‐Saint‐Etienne, CNRS, IOGS, Laboratoire Hubert Curien, UMR5516 St‐Etienne 42023 France
2. Univ Lyon Mines Saint‐Etienne, CNRS, Centre SMS, Laboratoire Georges Friedel, UMR5307 St‐Etienne 42023 France
3. Arizona Center for Mathematical Sciences and College of Optical Sciences University of Arizona Tucson AZ 85721 USA