Current-induced second harmonic generation in inversion-symmetric Dirac and Weyl semimetals

Second harmonic generation (SHG) is a fundamental nonlinear optical phenomenon widely used both for experimental probes of materials and for application to optical devices. Even-order nonlinear optical responses including SHG generally require the breaking of inversion symmetry, and thus have been utilized to study noncentrosymmetric materials. Here, we study theoretically the SHG in inversion-symmetric Dirac and Weyl semimetals under a DC current which breaks the inversion symmetry by creating a nonequilibrium steady state. Based on analytic and numerical calculations, we find that Dirac and Weyl semimetals exhibit strong SHG upon application of finite current. Our experimental estimation for a Dirac semimetal Cd3As2 and a magnetic Weyl semimetal Co3Sn2S2 suggests that the induced susceptibility chi((2)) for practical applied current densities can reach 10(5) pm V-1 with mid-IR or far-IR light. This value is 10(2)-10(4) times larger than those of typical nonlinear optical materials. We also discuss experimental approaches to observe the current-induced SHG and comment on current-induced SHG in other topological semimetals in connection with recent experiments.

Automated summary

Second harmonic generation (SHG) is a fundamental nonlinear optical phenomenon that has been widely studied for both experimental probes of materials and applications in optical devices. This study focuses on the theoretical analysis of SHG in inversion-symmetric Dirac and Weyl semimetals under the influence of a DC current, showing strong SHG effects upon the application of finite current. Experimental estimations suggest that Dirac and Weyl semimetals exhibit significantly higher induced susceptibility values compared to typical nonlinear optical materials.