Kramers Weyl semimetals as quantum solenoids and their applications in spin-orbit torque devices

Wen-Yu He,K T Law,Xiao Yan Xu

doi:10.1038/s42005-021-00564-w

Abstract

Kramers Weyl semimetals are Weyl semimetals that have Weyl points pinned at the time reversal invariant momenta. Recently it has been discovered that all chiral crystals host Weyl points at time reversal invariant momenta, so metals with chiral lattice symmetry all belong to the category of Kramers Weyl semimetals. In this work, we show that due to the chiral lattice symmetry, Kramers Weyl semimetals have the unique longitudinal magnetoelectric effect in which the charge current induced spin and orbital magnetization is parallel to the direction of the current. This feature allows Kramers Weyl semimetals to act as nanoscale quantum solenoids with both orbital and spin magnetization. As the moving electrons of Kramers Weyl semimetal can generate longitudinal magnetization, Kramers Weyl semimetals can be used for new designs of spin-orbit torque devices with all electric control of magnetization switching for magnets with perpendicular magnetic anisotropy.

Highlights

Kramers Weyl semimetals are Weyl semimetals that have Weyl points pinned at the time reversal invariant momenta
We point out that the chiral lattice symmetry in Kramers Weyl semimetals (KWS) brings about a unique property: an electric field applied along the principal symmetry axis of the crystal would induce spin and orbital magnetization which is parallel to the applied electric field
The little group at k0 is isomorphic to a chiral point group which guarantees detðvÞ ≠ 0 so that the Kramers Weyl point emerges at k = 0

Summary

Introduction

Kramers Weyl semimetals are Weyl semimetals that have Weyl points pinned at the time reversal invariant momenta. We show that due to the chiral lattice symmetry, Kramers Weyl semimetals have the unique longitudinal magnetoelectric effect in which the charge current induced spin and orbital magnetization is parallel to the direction of the current. It was shown that generally, due to the low lattice symmetry, band splittings appear away from time-reversal invariant points in momentum space and result in Kramers Weyl points pinned at time-reversal invariant momenta It is not clear how the properties of KWS are distinct from that of other Weyl semimetals with non-chiral point group symmetry. The new KWS based devices allow all electric control of magnetic switching for ferromagnets with perpendicular magnetic anisotropy, which is important for high density magnetic memories

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Conclusion