Spin excitations in the candidate Weyl semimetal EuCuAs

Very recently, EuCuAs was proposed as an example of a topological semimetal. Our measurements on Wish show that the Eu magnetic structure is incommensurate with a propagation vector q = (0, 0, 4.1). This was unexpected, as ab inito calculations had predicted a collinear antferromagnetic order. It is a very interesting discovery because it means that the conduction states experience a time-reversal-symmetry-breaking interaction, which could create a pair of Weyl points in the electronic band structure. We propose to measure the powder-averaged magnon spectrum on Merlin. The objective is to determine the dominant in-plane exchange interaction, which is needed to develop a spin Hamiltonian to understand the magnetic behaviour.