Center for Functional Nanomaterials Seminar

A ferro-rotational order describes a ferroically ordered state of an axial vector moment that is invariant under both spatial inversion and time reversal operations. This order was first theoretically proposed to complete the classification of ferroics with vector order parameters, and now is the last remaining class to be revealed after the discoveries of ferro-toroidal, ferromagnetic, and ferroelectric orders. More recently, this order is suggested to exist in a good number of complex oxides, and is considered to be responsible for several novel phenomena including the type-II multiferroic order. In this talk, I will present our studies of the ferro-rotational order in a type-II multiferroic material RbFe(MoO4)2 using high sensitivity rotational anisotropy second harmonic generation (RA SHG). I will show that the higher order electric quadrupole (EQ) contribution to SHG has been exploited to investigate this inversion-symmetry-preserved ferro-rotational order. I will then reveal several physical properties of this ferro-rotational order including its symmetry, domain distributions, temperature evolutions, and coupling field. I will further discuss the significance of understanding this ferro-rotational order and the opportunity brought by high sensitivity EQ SHG.