Topological phase transitions in Graphene under periodic kicking

Abstract

We consider a periodically $δ$-kicked Graphene system with the kicking applied in the $\hat{z}$ direction. This is known to open a gap at the Dirac points by breaking inversion symmetry through the introduction of a time-varying staggered sub-lattice potential. We look here at the topological properties of the gap closing-opening transition that occurs as functions of the driving amplitude. The dependence of the driving induced mass-term and the Berry curvature on the strength of the driving is computed. The Chern number for the gapped-out points is computed numerically and it's variation with the driving amplitude is studied. We observe that though the z-kicked Graphene system being time-reversal invariant remains topologically trivial in the bulk, it still permits a quantification of the topological changes that occur at individual gaps with changes in the sign of the mass term. Note:In Sec.II C,page 5, equations 10 & 11 have typos (in the denominators of these equations ,the parentheses appearing after $\cos^2(α_z)$ should appear before it).Eq.12 has a missing term which is independent of the wavevector.This follows from there being typos in eq.9 where in the numerators of the coefficients of $\hat{x}$ and $\hat{y}$ the $α_z$ multiplied to the second term has to be dropped in both cases.This follows through to eqs. 10,11 and 12.