Origin of the large topological Hall effect in the EuCd$_2$Sb$_2$ antiferromagnet

TL;DR

This paper investigates the origins of the large topological Hall effect in EuCd$_2$Sb$_2$, revealing that Weyl states and spin chirality contribute through different mechanisms below and above the Néel temperature.

Contribution

It identifies multiple mechanisms—Weyl states and scalar spin chirality—that contribute to the topological Hall effect in EuCd$_2$Sb$_2$, with distinct processes below and above the Néel temperature.

Findings

Weyl states are primary sources of Berry curvature below and above T_N.

Breaking of C3 symmetry below T_N creates Weyl nodes from Dirac points.

Spin fluctuations above T_N induce Weyl states, contributing to the Hall effect.

Abstract

We study the origin of large topological Hall effect in the single-crystalline EuCd$_2$Sb$_2$, which orders antiferromagnetically at the N\'eel temperature $T_{\rm N}=7.4$ K. Measurements of magnetoresistance and Hall resistivity disclose anomalies that evolve with temperature and magnetic field, closely tracking the magnetization process. Analysis of these data identifies three possible mechanisms responsible for the enhanced Berry curvature driving the observed topological Hall effect. Below and above $T_{\rm N}$, Weyl states are the main sources of large momentum-space Berry curvature, though their formation mechanisms differ in these two temperature ranges. Below $T_{\rm N}$, breaking of $C_{3}$ symmetry generates Dirac points that split into Weyl nodes in applied magnetic field, whereas above $T_{\rm N}$, strong spin fluctuations can induce Weyl states. The third contribution, which occurs below $T_{\rm N}$, arises from scalar spin chirality developing within antiferromagnetic domain walls, which generates a real-space Berry curvature.