1. School
of Mathematics, The University of Manchester, Manchester, M13 9PL, England
2. MackGraphe—Graphene
and Nano-Materials Research Center, Mackenzie Presbyterian University, Rua da Consolação 896, 01302-907, São Paulo, SP, Brazil
3. Department
of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542
4. Centre
for Advanced 2D Materials, National University of Singapore, 6 Science
Drive 2, Singapore 117546