Field-tunable Weyl points and large anomalous Hall effect in the degenerate magnetic semiconductor EuMg2Bi2

Magnets, with topologically nontrivial Dirac/Weyl points, have recently attracted significant attention owing to their unconventional physical properties, such as a large anomalous Hall effect. However, they typically have a high carrier density and a complicated band structure near the Fermi energy. In this Letter, we report a degenerate magnetic semiconductor EuMg2Bi2, which exhibits a single valley at the I' point, where field-tunable Weyl points form via a magnetic exchange interaction with the local Eu spins. By the high-field measurements on high-quality single crystals, we observed quantum oscillations in the resistivity, elastic constant, and surface impedance, which enabled us to determine the position of the Fermi energy E-F. In combination with a first -principles calculation, we revealed that the Weyl points are located in the vicinity of E-F when the Eu spins are fully polarized, leading to a peak of energy-dependent anomalous Hall conductivity due to the Berry curvature. Accordingly, in the forced ferromagnetic phase, we observed a large anomalous Hall effect (Hall angle (sic)(AH) similar to 0.07) qualitatively consistent with the calculation, which demonstrates a marked impact of the Weyl points in the simple band structure.

Automated summary

In this letter, we introduce a degenerate magnetic semiconductor EuMg2Bi2, which possesses topologically nontrivial Dirac/Weyl points formed by a magnetic exchange interaction with local Eu spins. Quantum oscillations in the resistivity, elastic constant, and surface impedance reveal the position of the Fermi energy EF and the existence of Weyl points near EF when the Eu spins are fully polarized, leading to an energy-dependent anomalous Hall conductivity peak. These findings are supported by first-principles calculations and demonstrate the significant impact of Weyl points on the simple band structure.