Second harmonic imaging of antiferromagnetic domains and confirmation of absence of ferroaxial twins in MnTiO3

Multipoles in a material, which describe the degrees of freedom of electrons, have recently attracted much attention from the perspective of a unified understanding of diverse physical phenomena. Therefore, demand has been increasing for probes that can detect various types of multipoles. Here, we report the detection of multiple multipoles in collinear antiferromagnet MnTiO₃ using optical second harmonic generation (SHG). Utilizing SHG selection rules and an imaging technique, we detect ferroaxial and antiferromagnetic orders and visualize their domains, and show that SHG is a powerful tool for the simultaneous observation of underlying multipoles with different symmetries.