Extended Data Fig. 2: Carrier-injection into bulk states and comparison of bulk- and surface-state HHG.
From: Tunable non-integer high-harmonic generation in a topological insulator
a, Calculated carrier density injected, within one THz half cycle, into the bulk conduction band by Zener tunnelling, as a function of the peak THz electric field. Red horizontal line: carrier density, nbulk, injected for ETHz = 3 MV cm−1. b, HH spectra, IHH, calculated by Boltzmann equations for massive electrons in the bulk crystal described by a cosine-shaped band structure (blue curve), and by Boltzmann equation for Dirac electrons in the surface state of a topological insulator. Inset: corresponding band structures for bulk (blue curve) and surface state electrons (red curve).
