Origin of the giant spin-phonon coupling in rare-earth halides

Explain quantitatively the magnitude of the giant spin-phonon coupling responsible for the large effective magnetic fields generated by chiral phonons in rare-earth halides.

Background

The paper describes a strong magnetic response generated by coherently excited chiral phonons in the paramagnetic rare-earth halide CeF3. The reported effective magnetic field reaches 0.9 T at relatively low optical fluence and is attributed to near-resonant coupling between phonons and crystal-electric-field levels.

Although this mechanism accounts qualitatively for the enhancement, the authors state that the size of the resulting spin-phonon coupling is not fully understood.