Magnetic order induces symmetry breaking in the single crystalline orthorhombic CuMnAs semimetal

TL;DR

This study reveals how magnetic ordering in orthorhombic CuMnAs induces symmetry breaking, leading to the opening of band gaps and affecting topological fermions, with implications for antiferromagnetic spintronics.

Contribution

It provides detailed magnetic phase transitions and symmetry analysis of orthorhombic CuMnAs, linking magnetic order to topological electronic properties.

Findings

Cu0.95MnAs is a commensurate antiferromagnet below 360 K.

Cu0.98Mn0.96As undergoes two magnetic phase transitions at 320 K and 230 K.

Magnetic order breaks key symmetries, opening band gaps and affecting topological fermions.

Abstract

Recently, orthorhombic CuMnAs has been proposed to be a magnetic material where topological fermions exist around the Fermi level. Here we report the magnetic structure of the orthorhombic Cu0.95MnAs and Cu0.98Mn0.96As single crystals. While Cu0.95MnAs is a commensurate antiferromagnet (C-AFM) below 360 K with a propagation vector of k = 0, Cu0.98Mn0.96As undergoes a second-order paramagnetic to incommensurate antiferromagnetic (IC-AFM) phase transition at 320 K with k = (0.1,0,0), followed by a second-order IC-AFM to C-AFM phase transition at 230 K. In the C-AFM state, the Mn spins order parallel to the b-axis but antiparallel to their nearest-neighbors with the easy axis along the b axis. This magnetic order breaks Ry gliding and S2z rotational symmetries, the two crucial for symmetry analysis, resulting in finite band gaps at the crossing point and the disappearance of the massless topological fermions. However, the spin-polarized surface states and signature induced by non-trivial topology still can be observed in this system, which makes orthorhombic CuMnAs promising in antiferromagnetic spintronics.