Magneto-optical Kramers-Kronig analysis

TL;DR

The paper introduces a simple, efficient magneto-optical experiment and a Kramers-Kronig analysis method (MOKKA) to extract complex dielectric functions for circular polarizations without circularly polarized light, applicable over broad frequencies.

Contribution

It presents a novel magneto-optical Kramers-Kronig analysis technique that simplifies measurements and can be used at high magnetic fields without rotating polarizers.

Findings

Successfully applied to bismuth and graphite

Enabled handedness-resolved magneto-absorption spectra of graphene

Allows in-situ measurements with fixed polarizers

Abstract

We describe a simple magneto-optical experiment and introduce a magneto-optical Kramers-Kronig analysis (MOKKA) that together allow extracting the complex dielectric function for left- and right-handed circular polarizations in a broad range of frequencies without actually generating circularly polarized light. The experiment consists of measuring reflectivity and Kerr rotation, or alternatively transmission and Faraday rotation, at normal incidence using only standard broadband polarizers without retarders or quarter-wave plates. In a common case, where the magneto-optical rotation is small (below $\sim$ 0.2 rad), a fast measurement protocol can be realized, where the polarizers are fixed at 45$^\circ$ with respect to each other. Apart from the time-effectiveness, the advantage of this protocol is that it can be implemented at ultra-high magnetic fields and in other situations, where an \emph{in-situ} polarizer rotation is difficult. Overall, the proposed technique can be regarded as a magneto-optical generalization of the conventional Kramers-Kronig analysis of reflectivity on bulk samples and the Kramers-Kronig constrained variational analysis of more complex types of spectral data. We demonstrate the application of this method to the textbook semimetals bismuth and graphite and also use it to obtain handedness-resolved magneto-absorption spectra of graphene on SiC.