[摘要]：Coherent epitaxial YMnO3 ultrathin films have been built and their symmetries were studied using second harmonic generation techniques. The underlying symmetry, trigonality, was revealed by the pseudomorphic strain effect and a new in-plane component with six-fold symmetry emerges in addition to usual polarization along c-axis. Its in-plane anisotropy provides possible multiple states which is significant for its potential applications.
