Polaronic Enhancement of Second-Harmonic Generation in Lithium Niobate

Abstract

Density-functional theory within a Berry-phase formulation of the dynamical polarization is used to determine the second-order susceptibility ${\chi }^{(2)}$ of lithium niobate (LiNbO${}_3$). Defect trapped polarons and bipolarons are found to strongly enhance the nonlinear susceptibility of the material, in particular if localized at Nb${}_{\mathrm{V}}$-V${}_{\mathrm{Li}}$ defect pairs. This is essentially a consequence of the polaronic excitation resulting in relaxation-induced gap states. The occupation of these levels leads to strongly enhanced ${\chi }^{(2)}$ coefficients and allows for the spatial and transient modification of the second-harmonic generation of macroscopic samples.

5 pages, 6 figures

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