Chirality and magnetism: Free electron on an infinite helix, NCD, MCD, and magnetochiral dichroism

The free electron on a helix with periodic boundary conditions is undoubtedly one of the simplest quantum chemical models exhibiting both chirality and orbital angular momentum. Subjected to a light beam traveling parallel to the helix axis, the model exhibits natural circular dichroism and, assuming a lifting of the magnetic degeneracy by an external static magnetic field, also magnetic circular dichroism and magnetochiral dichroism. We believe that the model illustrates well the interplay of chirality and magnetism in a pure magnetic state, and that it could also be of interest in the study of the recently discovered chiral ferromagnets.