Magneto-chiral birefringence and dichroism

TLDR

The absorption coefficient of a chiral molecule is predicted to shift slightly when a magnetic field is applied parallel to the light beam, regardless of polarization. The study extends this idea by exploring analogous refractive‑index shifts and situating magneto‑chiral effects within the framework of time‑odd components of complex optical activity tensors. The authors derive explicit expressions for the refractive‑index and absorption‑coefficient differences of chiral molecules in parallel versus antiparallel magnetic fields, introduce magneto‑chiral Faraday A‑, B‑, and C‑terms, and assess the feasibility of detecting these dichroic terms in various chiral molecules. A rough estimate suggests magneto‑chiral birefringence could be detected with a modified Rayleigh refractometer, and the magneto‑chiral observables are shown to transform as time‑odd polar vectors.

Abstract

It was pointed out recently that the absorption coefficient of a chiral molecule should be shifted slightly in a magnetic field parallel to a light beam in any polarization state. This suggestion is developed further by considering an analogous refractive index shift and by discussing these magneto-chiral phenomena in the unified context of effects generated by the ‘magnetic’ (time-odd) parts of the complex optical activity tensors. Explicit expressions, in terms of molecular property tensors, are derived for the difference in refractive index and absorption coefficient of a chiral molecule in a magnetic field parallel and antiparallel to the light beam, and magneto-chiral analogues of the Faraday A-, B- and C-terms introduced. A rough estimate of the magneto-chiral birefringence indicates that it should be observable using a modified Rayleigh refractometer. The feasibility of observing magneto-chiral dichroism A-, B- and C-terms in different types of chiral molecules is also considered. The magneto-chiral observables are shown to transform as time-odd polar vectors.