Interband-polarization dominated high harmonic generation from flat-band NbOCl2 materials in strong laser fields

High harmonic generation (HHG) in solids is sensitively dependent on the band dispersions of crystals, which involves intraband and interband processes in conventional semiconducting materials. Here, we numerically simulate the HHG from a two-dimensional (2D) NbOCl2 material of a flat valence band in strong midinfrared laser fields, which shows special harmonic signals that are predominantly originated from interband polarization. The suppressed intraband HHG is mainly attributed to its intrinsic heavy carrier with large effective mass. By bending the flat band under strain engineering, the HHG spectra of strained 2D NbOCl2 demonstrate typical features with below-gap harmonics and high-energy harmonics dominated by intraband and interband processes, respectively. In addition, 2D NbOCl2 exhibits low exfoliation energy, excellent dynamical and thermal stability, and desirable optical property, which endow it with more experimental feasibilities. locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon Physics Subject Headings (PhySH)PhotocurrentLayered semiconductorsHigh-harmonic generation