Observation of chiral phonons in an ilmenite with a ferro-rotational order

A chiral structure is non-superimposable on its mirror image and possesses a well-defined handedness. Chirality characterizes the asymmetry between a structure and its mirror image and plays a crucial role across various scientific fields, including physics, chemistry, and biology. This concept also extends to elementary particles and quasiparticles as a quantum property. For example, lattice vibrations in the form of chiral phonons can carry angular momentum and, consequently, a magnetic moment. In many cases, chiral phonons arise from crystal chirality. In this talk, we will present measurements of resonant inelastic X-ray scattering (RIXS) that reveal the existence of chiral phonons in MnTiO₃, an ilmenite material whose order parameter is a ferroaxial moment with a rotational electric-dipole arrangement. We will discuss the circular dichroism observed in the RIXS excitations of these ferro-rotational chiral phonons.