Phase-sensitive second-harmonic microscopy reveals polarity of topologically centrosymmetric molecular crystals

Abstract

Phase-sensitive second-harmonic microscopy is applied to reveal grow-in polarity in topologically centrosymmetric crystals of 4-chloro-4′-nitrostilben. As predicted by the Markow model of layer-by-layer polarity formation, growth along + and −b-direction in P21/c is producing optical nonlinearity in both sectors associated with the b axis. Present experiments show that formation of a pyroelectric symmetry class is a stochastic property of molecular crystals grown from dipolar compounds and near to thermodynamic equilibrium.