Second harmonic generation in the tilted type-I Dirac metals under terahertz frequency regime

Abstract

Abstract In this work, we theoretically demonstrate that the second order response can survive in a two-dimensional (2D) tilted type-I Dirac metal due to the time reversal symmetry (TRS) breaking. We find that, in the terahertz regime, the second harmonic generation (SHG) is appreciably strong and is widely depending on the tilting parameter, temperature, excitation frequency and the applied electric field, respectively. By comparing with the first and third order optical response, we also note that each of the three modes of optical response dominates in different frequency intervals in accordance with the strength of the applied electric field. With the help of the ω − E c diagram (with ω and E c being the excitation frequency and the critical electric field, respectively), we are able to engineer the desired nonlinear response by varying the excitation frequency and the strength of the applied electric field. Finally, we briefly discuss on the influences of relaxation time on SHG by considering four types of k-dependent scattering mechanisms.