Magnetic Photocurrents in Multifold Weyl Fermions

TL;DR

This paper investigates the magneto-optical response of chiral multifold fermions, demonstrating their suitability for observing the Helical Magnetic Effect (HME), which is related to circular photogalvanic effects and persists even with realistic complexities.

Contribution

The study derives an analytical expression for the HME in multifold fermions and shows it can be comparable to known photogalvanic effects, highlighting their potential for experimental observation.

Findings

HME is present in multifold fermions with linear, symmetric dispersion.

The HME photocurrent can be similar in magnitude to the circular photogalvanic effect.

Non-linear and symmetry-breaking terms do not prevent observing the HME.

Abstract

We examine the magneto-optical response of chiral multifold fermions. Specifically, we show that they are ideal candidates for observing the Helical Magnetic Effect (HME) previously predicted for simple Weyl fermions. Unlike Weyl fermions, the HME is present in multifold fermions even in the simplest case where the low-energy dispersion is linear and spherically symmetric. In this ideal case, we derive an analytical expression for the HME and find it is proportional to the circular photogalvanic effect; for realistic parameters and accounting for the geometry of the setup, the HME photocurrent could be roughly the same order of magnitude as the circular photogalvanic effect observed in multifold fermions. Additional non-linear and symmetry-breaking terms will ruin the quantization but not hurt the observation of the HME.