Tunable colossal negative magnetoresistance of topological semimetal EuB₆ thin sheets

EuB₆, a magnetic topological semimetal, has attracted considerable attention in recent years due to its rich intriguing physical properties, including a colossal negative magnetoresistance (CNMR) ratio exceeding −80%, a topological phase transition and a predicted quantum anomalous Hall effect (QAHE) approaching the two-dimensional (2D) limit. Yet, studies of the influence of the dimensionality approaching 2D on the electronic transport properties of EuB₆ are still scarce. In this work, EuB₆ thin sheets with thicknesses ranging from 35 μm to 180 μm were successfully fabricated through careful mechanical polishing of high-quality EuB₆ single crystals. The reduced thickness, temperature and magnetic field have a strong influence on the electronic transport properties, including the CNMR and carrier concentration of EuB₆ thin sheets. As the thickness of EuB₆ thin sheets decreases from 180 μm to 35 μm, the magnetization transition temperature and the corresponding suppressing temperature of the Kondo effect decrease from 15.2 K to 10.9 K, while the CNMR ratio increases from −87.2% to −90.8%. Furthermore, the weak antilocalization effect transits to a weak localization effect and the carrier concentration increases by 9.4% at 30 K in a 35 μm EuB₆ thin sheet compared to the value reported for a 180 μm thin sheet. Our findings demonstrate an obvious tunable effect of the reduced dimensionality on the transport properties of EuB₆ along with the temperature and magnetic field, which could provide a route to exploring the QAHE near the 2D limit in EuB₆ and other topological semimetals.