Ferromagnetic-electrodes-induced Hall effect in topological Dirac semimetals

TL;DR

This paper predicts an unconventional Hall effect in topological Dirac semimetals induced by ferromagnetic electrodes, breaking time-reversal symmetry and resulting in a large, robust Hall response useful for spin state detection.

Contribution

It introduces a novel Hall effect mechanism in topological semimetals caused by ferromagnetic electrodes, with detailed theoretical modeling and potential applications.

Findings

Hall angle comparable to quantum Hall states with full spin polarization

Effect persists despite impurities, indicating robustness

Can distinguish parallel and antiparallel magnetization configurations

Abstract

We propose an unconventional type of Hall effect in a topological Dirac semimetal with ferromagnetic electrodes. The topological Dirac semimetal itself has time-reversal symmetry, whereas attached ferromagnetic electrodes break it, causing the large Hall response. This induced Hall effect is a characteristic of the helical surface/edge states that arise in topological materials, such as topological Dirac semimetals or quantum spin Hall insulators. We compute the Hall conductance/resistance and the Hall angle by using a lattice model with four-terminal geometry. For topological Dirac semimetals with four electrodes, the induced Hall effect occurs whether the current electrodes or the voltage electrodes are ferromagnetic. When the spins in electrodes are almost fully polarized, the Hall angle becomes as large as that of quantum Hall states or ideal magnetic Weyl semimetals. We show the robustness of the induced Hall effect against impurities and also discuss the spin injection and spin decay problems. This Hall response can be used to detect whether the magnetizations of the two ferromagnetic electrodes are parallel or antiparallel.