Double resonant tunable second harmonic generation in two-dimensional layered materials through band nesting

We proposed a mechanism to generate giant anisotropic second harmonic nonlinear response via double resonance effect, achieved through band nesting electronic band-structure engineering. The ideal setup would be triplet of nested bands separated by the fundamental energy $\ensuremath{\hbar}\ensuremath{\omega}$. demonstrate theoretically that phenomenon can realized in bilayer SnS tuning with perpendicular electrical bias, which maximizes susceptibility several orders magnitude. Moreover, tunability polarization anisotropy useful for realizing novel polarization-sensitive devices.