Magnetic field-induced topological phase transition for colossal negative magnetoresistance in EuB6

EuB6, as a magnetic Weyl semimetal, has attracted much attention in recent years due to its rich intriguing physical properties, especially the colossal negative magnetoresistance (CNMR) exceeding -80% and the topological phase transition. Yet, the underlying mechanism of the CNMR in EuB6 is still controversial. In this work, the CNMR with a maximum value of -88.4% and Hall resistivity without linear dependence on the magnetic field are both observed to indicate the existence of a weak ferromagnetic order below 50 K. The effective carrier concentration can be modulated by both temperatures and external magnetic fields. Moreover, the angle-resolved photoelectron spectroscopy results demonstrate the gradual band splitting and crossing near the Fermi level below 15 K, and the field-dependent Kelvin probe force microscope results confirm the field-induced variation of the Fermi level at different temperatures. Furthermore, by integrating those results with the monotonic increment relationship between the effective carrier concentration and the field-induced magnetization ratio, it is concluded that the magnetic field-induced topological phase transition is the main mechanism for the CNMR in EuB6, which is helpful to understand the exotic transport properties in magnetic topological materials. Our findings provide a route for exploring and manipulating the topology-related transport properties via the external magnetic field in other systems with strong correlation between magnetism and topological states.