Topological Charge Quadrupole Protected by Spin-Orbit U(1) Quasi-Symmetry in Antiferromagnet NdBiPt

TL;DR

This paper predicts a new quasiparticle called topological charge quadruple in NdBiPt, protected by spin-orbit quasi-symmetry, leading to large nonlinear Hall effects and opening new avenues in topological material design.

Contribution

It introduces the concept of topological charge quadruple protected by spin-orbit U(1) quasi-symmetry in antiferromagnetic NdBiPt, a novel quasiparticle with unique topological properties.

Findings

Prediction of topological charge quadruple in NdBiPt.

Protection of TCQ by spin-orbit U(1) quasi-symmetry.

Large Berry curvature dipole causing nonlinear Hall effect.

Abstract

The interplay of symmetry and topology in crystal solids has given rise to various elementary excitations as quasiparticles. Among these, those with significant Berry-phase-related transport responses are of particular interest. Here, we predict a new type of quasiparticle called topological charge quadruple (TCQ), which is analogous to a charge quadrupole but consists of two closely-packed pairs of Weyl points in momentum space, specifically in a half-Heusler antiferromagnet NdBiPt. Interestingly, the TCQ is protected by the spin-orbit $U(1)$ quasi-symmetry, rather than any exact crystallographic symmetries. This quasi-symmetry restricts the energy splitting induced by symmetry-lowering perturbations to a second-order effect. Furthermore, the closely located Berry curvature sources and sinks in the TCQ lead to a large Berry curvature dipole, resulting in a significant nonlinear Hall effect. Our work opens an avenue for designing novel quasiparticles using quasi-symmetries and developing materials with enhanced nonlinear responses.