2D Materials: A Wonderland of Nonlinear Optical Responses

Materials with strong nonlinear optical (NLO) responses are crucial for many technologically important applications. NLO responses are governed by intrinsic symmetry, transition dipole moments, local environment and dimensionality. I will present our recent first-principles theoretical discoveries and understandings of giant NLO responses in a number of 2D materials, and demonstrate that 2D materials provide perfect solid-state platform for exploring nonlinear nanooptics. Transition metal dichalcogenides and group IV monochalcogenides possess strong second order NLO responses, and the latter also hold giant ferroelectric-ferroelastic multiferroicity which is directly correlated with their NLO properties. We will present recent work on other 2D NLO properties and discuss the relationship between NLO responses and Berry connections. Our present findings open up new avenues for ultrathin nonlinear optoelectronics. References: 1) Giant Optical Second Harmonic Generation in Two-Dimensional Multiferroics. Nano Letters 17, 5027-5034 (2017). 2) Two-dimensional multiferroics in monolayer group IV monochalcogenides. 2D Materials 4, 015042 (2017). 3) Nonlinear Optical Responses in 2D Materials. to be submitted (2017).