Second-harmonic near-field imaging of ferroelectric domain structure of YMnO3

By: C. C. Neacsu, B. B. van Aken, M. Fiebig, and M. B. Raschke

Physical Review B 79, 100107(R) (2009)

Near-field tip-enhanced and symmetry-selective nonlinear light scattering is demonstrated for imaging nanoscopic ferroelectric order. The surface topology of antiparallel ferroelectric domains in multiferroic YMnO3 is spatially resolved by second-harmonic generation (SHG). Optical phase contrast is obtained by interference between the local near-field SHG and a self-homodyne far-field reference SHG field. Ferroelectric domains anisotropically elongated along the hexagonal crystallographic axis were found, with typical dimensions of ∼1000 x 200 nm2. The irregular domain shapes seem to contrast the behavior of ordinary ferroelectrics. Relying on symmetry properties only, SHG scattering-type scanning near-field optical microscopy can be extended to probe any ferroic order.