Strain-Induced Giant Second-Harmonic Generation In Monolayered 2h-Mox2 (X = S, Se, Te)

Dynamic second-order nonlinear susceptibilities, chi((2))(2 omega, omega, omega) chi((2)) (omega), are calculated here within a fully first-principles scheme for monolayered molybdenum dichalcogenides, 2H-MoX2 (X = S, Se, and Te). The absolute values of chi((2)) (omega) across the three chalcogens critically depend on the band gap energies upon uniform strain, yielding the highest chi((2)) (0) similar to 140 pm/V for MoTe2 in the static limit. Under this uniform in-plane stress, 2H-MoX2 can undergo direct-to-indirect transition of band gaps, which in turn substantially affects chi((2)) (omega). The tunability of chi((2)) (omega) by either compressive or tensile strain is demonstrated especially for two important experimental wavelengths, 1064 nm and 800 nm, where resonantly enhanced non-linear effects can be exploited: chi((2)) of MoSe2 and MoTe2 approach similar to 800 pm/V with -2% strain at 1064 nm. (C) 2015 AIP Publishing LLC.