Shubnikov–de Haas oscillations and electronic features in the ferromagnetic semimetal EuAl2Ge2

Abstract

Magnetic topological compounds offer an ideal platform for studying the complex interplay between intrinsic magnetism, symmetry breaking, and band topology. Herein, we grew EuAl2Ge2 single crystals and investigated their electronic features via quantum oscillations and theoretical calculations. This compound exhibits an antiferromagnetic ground state below 27.6 K, and a field-induced transition to a ferromagnetic phase with distinct anisotropy. Clear Shubnikov–de Haas oscillations observed in the ferromagnetic regime disclose a multi-sheet Fermi surface with significant c-axis elongation, further corroborated by angular magnetoresistance measurements and theoretical calculations. Crucially, the nonmagnetic phase harbors two symmetry-protected pairs of Dirac points, whereas ferromagnetic order drives distinct topological electronic phases: out-of-plane magnetization preserves C3z symmetry and yields multiple Weyl nodes, while in-plane magnetization breaks rotational symmetry and causes a reduced Weyl state. Our results establish EuAl2Ge2 as a promising platform for achieving direct magnetic control over band topology and exploring tunable topological quantum phases.