Magnetism and anomalous transport in the Weyl semimetal PrAlGe: possible route to axial gauge fields

Daniel Destraz,Joachim Kohlbrecher,Stepan S Tsirkin,Lakshmi Das,Jonathan S White,Pascal Puphal,Adolfo G Grushin,Ekaterina Pomjakushina,J Chang,Titus Neupert,Yang Xu,A Schilling,Lukas Keller

doi:10.1038/s41535-019-0207-7

Abstract

In magnetic Weyl semimetals, where magnetism breaks time-reversal symmetry, large magnetically sensitive anomalous transport responses are anticipated that could be useful for topological spintronics. The identification of new magnetic Weyl semimetals is therefore in high demand, particularly since in these systems Weyl node configurations may be easily modified using magnetic fields. Here we explore experimentally the magnetic semimetal PrAlGe, and unveil a direct correspondence between easy-axis Pr ferromagnetism and anomalous Hall and Nernst effects. With sizes of both the anomalous Hall conductivity and Nernst effect in good quantitative agreement with first principles calculations, we identify PrAlGe as a system where magnetic fields can connect directly to Weyl nodes via the Pr magnetisation. Furthermore, we find the predominantly easy-axis ferromagnetic ground state co-exists with a low density of nanoscale textured magnetic domain walls. We describe how such nanoscale magnetic textures could serve as a local platform for tunable axial gauge fields of Weyl fermions.

Highlights

With CeAlGe13 and LaAlGe14 respectively proposed to be magnetic and nonmagnetic type-II Weyl semimetals, PrAlGe is expected to be a magnetic type-I Weyl semimetal with spaceinversion symmetry broken by the polar lattice symmetry, and time-reversal symmetry broken at the onset of an easy-axis ferromagnetic ordering along c (Fig. 1a).[12]
An observable consequence is the emergence of anomalous Hall conductivity (AHC) in the plane normal to the direction of the magnetisation, which is due to the associated Berry curvature that remains finite when evaluated over the Brillouin zone below the Fermi energy
Upon cooling below Tc, extra scattered intensity due to magnetism appears at scattering angles commensurate with the tetragonal point symmetry of the PrAlGe lattice, and can be described by a propagation vector Q = 0

Summary

INTRODUCTION

In Dirac and Weyl semimetals, the emergence of large Berry curvatures due to electron band degeneracies, or singular band touching points (Weyl nodes), leads to striking topological effects on conduction electrons[1,2] that can be detected by measurements of negative magnetoresistance,[3] and the anomalous Hall effect (AHE).[4,5] In magnetic semimetals, it is known that both the size and direction of the magnetisation can generate Weyl nodes and shift their positions, which provides the possibility for magnetic field control of the Weyl node positions and the emergence of the AHE, a critical aspect of the nascent field of topological electronics.[6]. Weyl-node induced Berry curvature in magnetic systems include antiferromagnetic (AFM) Mn3Sn,[7,8] kagome ferromagnetic (FM) semimetal Co3Sn2S2,5 and the topological nodal line ferromagnetic semimetal Fe3GeTe2.9 other works have connected the anomalous Nernst effect to the Berry curvature.[10,11] In these studies, a theoretical description of the observations provides the direct link between topological properties of the band structure and magnetically sensitive observables. This motivates both experiments and computational material science aimed at the rational engineering of band structures and the prediction of new systems with magnetically sensitive topological properties. PrAlGe is a magnetic Weyl semimetal that displays controllable transverse electronic responses using low applied magnetic fields that couple to the Pr magnetisation

RESULTS

DISCUSSION

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