[1] Univ Nova Lisboa, Dept Ciencia Mat, P-2829516 Caparica, Portugal
[2] Inst Super Engn Lisboa, P-1950062 Lisbon, Portugal
[3] Univ Lisbon, Ctr Fis Teor & Computac, P-1649003 Lisbon, Portugal
[4] Inst Super Tecn, Dept Fis, P-1049001 Lisbon, Portugal
[5] Inst Super Tecn, Inst Ciencia & Engn Mat & Superficies, P-1049001 Lisbon, Portugal
[6] Univ Cambridge, Cavendish Lab, Cambridge CB3 OHE, England