Fig. 1: Circular intensity difference (CID) in second harmonic generation (SHG) from ferroaxial materials. | npj Quantum Materials

Fig. 1: Circular intensity difference (CID) in second harmonic generation (SHG) from ferroaxial materials.

From: Three-dimensional imaging of ferroaxial domains using circularly polarized second harmonic generation microscopy

Fig. 1

a, b Schematic illustrations of a pair of ferroaxial domain states with the opposite sign of ferroaxial moment A defined as \({{{\mathbf{A}}}} \propto \mathop {\sum}\nolimits_i {{{{\mathbf{r}}}}_i \times {{{\mathbf{p}}}}_i}\). Here ri denotes a position vector of electric dipole pi from the symmetrical center of a structural unit. c, d Simplified c-axis views of a pair of ferroaxial domain states (A+ and A− domains) in NiTiO3. e, f Conceptual diagram of CID-SHG from A+ and A− domain states. The red and light green arrows denote fundamental circularly polarized light and SHG, respectively. The size of the light green arrows represents the intensity of SHG. Thus, the intensity of SHG from a ferroaxial material depends on both the circular polarization of fundamental light and the sign of A.

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