Creating and controlling Dirac fermions, Weyl fermions, and nodal lines in the magnetic antiperovskite Eu$_3$PbO

TL;DR

This paper reports the discovery of Eu$_3$PbO as a magnetic topological semimetal with multiple controllable topological phases, including Dirac, Weyl, and nodal line states, driven by magnetic order and external magnetic fields.

Contribution

It combines experimental and theoretical methods to identify Eu$_3$PbO as a new topological magnetic semimetal with tunable phases, expanding the family of magnetic topological materials.

Findings

Eu$_3$PbO hosts multiple topological phases with magnetic order.

External magnetic fields can control the topological phase transitions.

The study provides detailed band structure and surface state characterizations.

Abstract

The band topology of magnetic semimetals is of interest both from the fundamental science point of view and with respect to potential spintronics and memory applications. Unfortunately, only a handful of suitable topological semimetals with magnetic order have been discovered so far. One such family that hosts these characteristics is the antiperovskites, A$_3$BO, a family of 3D Dirac semimetals. The A=Eu$^{2+}$ compounds magnetically order with multiple phases as a function of applied magnetic field. Here, by combining band structure calculations with neutron diffraction and magnetic measurements, we establish the antiperovskite Eu$_3$PbO as a new topological magnetic semimetal. This topological material exhibits a multitude of different topological phases with ordered Eu moments which can be easily controlled by an external magnetic field. The topological phase diagram of Eu$_3$PbO includes an antiferromagnetic Dirac phase, as well as ferro- and ferrimagnetic phases with both Weyl points and nodal lines. For each of these phases, we determine the bulk band dispersions, the surface states, and the topological invariants by means of $\textit{ab-initio}$ and tight-binding calculations. Our discovery of these topological phases introduces Eu$_3$PbO as a new platform to study and manipulate the interplay of band topology, magnetism, and transport.