Magnetic and Optical Response of Chiral Fermions

TL;DR

This paper explores the magnetic and optical responses of chiral fermions in Dirac and Weyl materials, proposing mechanisms for magnetic photocurrents, analyzing quantum oscillations, and explaining THz emission phenomena.

Contribution

It introduces three mechanisms for magnetic photocurrents in chiral fermions, analyzes quantum oscillations with phase differences, and explains THz emission in TaAs.

Findings

Three mechanisms for magnetic photocurrents are proposed.

Quantum oscillations show a phase difference from Ohmic current.

External magnetic fields can differentiate left and right-handed fermions.

Abstract

Dirac and Weyl materials possess chiral fermions, which are characterized by nontrivial topology and large Berry curvature. Chiral fermions have nontrivial interactions with magnetic fields and light. In this work, we propose three different mechanisms for magnetic photocurrents caused by chiral fermions, with different requirements on the symmetry group of the crystal. We also study quantum oscillations of the anomalous current in the presence of a magnetic field, showing it has a different phase from the Ohmic current. We formulate a mechanism for THz emission observed in TaAs in response to ultrafast pulses. We propose a strain-induced anomalous current. We also show that an external magnetic field can create a difference between left and right handed fermions, which can be controlled by changing the field.