Magnetic tuning of band topology evidenced by exotic quantum oscillations in the Dirac semimetal EuMnSb2

Interplay between magnetism and electronic band topology is of central current interest in topological matter research. We use quantum oscillations as a powerful tool to probe the evolution of band topology in the Dirac semimetal ${\mathrm{EuMnSb}}_{2}$. The Eu local $4f$ magnetic moments display different antiferromagnetic states below 25 K and a field-polarized phase above 16 T. Upon cooling from 65 K into the field-polarized state, an exotic temperature-dependent shift of oscillation peaks arises, accompanied by the development of nonzero Berry phase and a huge unconventional splitting of the oscillations. Band-structure calculations confirm the change from trivial to nontrivial band topology induced by the ferromagnetic Eu state, classifying ${\mathrm{EuMnSb}}_{2}$ as a unique magnetic topological semimetal.