Single crystalline orthorhombic GdAlGe as a rare earth magnetic Dirac nodal-line metal

TL;DR

This study reports the discovery of orthorhombic GdAlGe as a magnetic Dirac nodal-line metal with unique electronic and magnetic properties, achieved through chemical pressure-induced structural transition from a Weyl semimetal.

Contribution

It demonstrates how chemical pressure induces a structural transition to an orthorhombic phase with magnetic topological features in GdAlGe, a novel magnetic Dirac nodal-line metal.

Findings

Hosts an antiferromagnetic ground state with two orderings at 35 K and 30 K

Exhibits a large magnetoresistance of ~100% at 2 K and 14 T

Shows Dirac-like linear band dispersion over 1.5 eV energy range

Abstract

Crystal engineering is a method for discovering new quantum materials and phases, which may be achieved by external pressure or strain. Chemical pressure is unique in that it generates internal pressure perpetually to the lattice. As an example, GdAlSi from the rare-earth ($R$) $R$Al$X$ ($X =$ Si or Ge) family of Weyl semimetals is considered. Replacing Si with the larger isovalent element Ge creates sufficiently large chemical pressure to induce a structural transition from the tetragonal structure of GdAlSi, compatible with a Weyl semimetallic state, to an orthorhombic phase in GdAlGe, resulting in an inversion-symmetry-protected nodal-line metal. We find that GdAlGe hosts an antiferromagnetic ground state with two successive orderings, at $T_\mathrm{N1}$ = 35 K and $T_\mathrm{N2}$ = 30 K. In-plane isothermal magnetization shows a magnetic field induced metamagnetic transition at 6.2 T for 2 K. Furthermore, electron-hole compensation gives rise to a large magnetoresistance of $\sim 100\%$ at 2 K and 14 T. Angle-resolved photoemission spectroscopy measurements and density functional theory calculations reveal a Dirac-like linear band dispersion over an exceptionally large energy range of $\sim$ 1.5 eV with a high Fermi velocity of $\sim 10^6$ m/s, a rare feature not observed in any magnetic topological materials.