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 $\omega -E_c$ diagram (with$\omega$ 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.

在这项工作中，我们从理论上证明了由于时间反转对称性（TRS）的破坏，二阶响应可以在二维（2D）倾斜的I型Dirac金属中幸存。我们发现，在太赫兹状态下，二次谐波（SHG）相当强，并且分别取决于倾角参数，温度，激励频率和所施加的电场。通过与一阶和三阶光学响应进行比较，我们还注意到，根据所施加电场的强度，光学响应的​​三种模式中的每一种都在不同的频率间隔中占优势。借助$\omega -{Ë}_C$ 图（带$\omega$ 和 ${Ë}_C$分别是激励频率和临界电场），我们能够通过改变激励频率和所施加电场的强度来设计所需的非线性响应。最后，我们通过考虑四种类型的与k有关的散射机制，简要讨论了弛豫时间对SHG的影响。