Nonlinear optical response of a Type-II Weyl semimetal

We investigate nonlinear optical responses in the type-I and -II Weyl semimetal using time-dependent Dirac equations which found good agreement with Kubo formula. As a comparison with type-I, we reveal that strong DC current in type-II semimetal is caused by the inversion symmetry breaking of the electron pockets. Furthermore the superposition of currents in the electron pocket bands weaken the AC contributions, due to the opposed-phase interference in time domain. We also verified the even-order high harmonic generations (HHGs) in anisotropic Type-I and -II semimetals at non-zero chemical potential. The symmetry analysis is applied to explain the unusual HHGs excited by the circularly polarized light. We provide a systematic study on tilted dirac cones.