High-harmonic generation in Dirac metals: Application of the semiconductor-Bloch formalism to topological systems

The generation of high-order harmonic radiation from the interaction of intense light waves with electrons in a solid has been a key observation coming from recent advancements in time-resolved spectroscopy. These high-harmonics provide a window into sub-cycle dynamics of the system and can provide insights to material properties. The semiconductor-Bloch formalism has seen success in describing high-harmonic generation (HHG) theoretically in semiconductor materials but topological effects are still not fully understood. Here we investigate these topological effects via a simulation of the semiconductor-Bloch equations. We compare the emission spectra of typical bulk and surface state Hamiltonians and find that the properties of the HHG are in good agreement with analytic considerations as well as recent experimental evidence.