Collapsing of Spin-Split Fermi Surfaces in the Magnetic Weyl Semimetal EuAuSb

Magnetic Weyl semimetals provide a rich platform for studying the coupling between localized magnetism and itinerant electrons. EuAuSb exhibits in-plane ferromagnetism and an interlayer helical order below 3.9 K, which breaks time-reversal symmetry and induces spin-split Fermi surfaces. In this talk, we report a rare example of exchange-coupling driven Fermi-surface collapse, revealed by temperature-dependent Shubnikov–de Haas quantum oscillations. Two distinct quantum oscillation frequencies (165 T and 80 T) observed at 2 K gradually merge into a single frequency near 40 K, indicating that the spin-split Fermi pockets collapse as short-range magnetic correlations weaken. Magnetization measurements confirm persistent magnetic correlations far above T_N, suggesting that the exchange interaction between Eu 4f moments and conduction electrons governs the observed Fermi-surface reconstruction.