Strong-field physics in three-dimensional topological insulators

We investigate theoretically the strong-field regime of light-matter interactions in topological-insulator class quantum materials. In particular, we focus on process non-perturbative high-order harmonic generation from paradigmatic three-dimensional topological insulator bismuth selenide (Bi$_2$Se$_3$) subjected to intense mid-infrared laser fields. analyze contributions spin-orbit-coupled bulk states and surface bands separately reveal a major difference how their yields depend ellipticity field. Bulk harmonics show monotonous decrease yield as increases, manner reminiscent high gaseous media. However, contribution exhibits highly non-trivial dependence, culminating with maximum for circularly polarized attribute observed anomalous behaviour to: (i) enhanced amplitude circular pattern interband dipole Berry connections vicinity Dirac point; (ii) influence higher-order, "hexagonal warping" terms Hamiltonian, which are responsible hexagonal deformation energy at higher momenta. The latter associated directly spin-orbit-coupling parameters. Our results thus establish sensitivity driven emission topology band structure well manifestations spin-orbit interaction.