1. Department
of Physics, King’s College London, Strand, London WC2R 2LS, United Kingdom
2. CNR-Istituto
Nanoscienze, Euromediterranean Center for Nanomaterial Modelling and Technology (ECMT), via Arnesano, I-73100 Lecce, Italy
3. Dipartimento
di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, via Arnesano I-73100 Lecce, Italy