Two types of colossal magnetoresistance with distinct mechanisms in Eu5In2As6

Recent reports of colossal negative magnetoresistance (CMR) in a few magnetic semimetals and semiconductors has attracted attention, because these materials are devoid of the conventional mechanisms of CMR such as mixed valence, double exchange interaction, and Jahn-Teller distortion [1]. New mechanisms have thus been proposed, including topological phase transition [2], ferromagnetic clusters [3], orbital currents [4], and charge ordering [5]. The CMR in these compounds have been reported in two general forms of either a resistivity peak or a resistivity upturn, which is suppressed by a magnetic field. Here we reveal both types of CMR in a single antiferromagnetic semiconductor Eu5In2As6. Using the transport and thermodynamic measurements, we show that the peak-type CMR is due to the formation of magnetic polarons, and the upturn-type CMR is due to charge segregation or charge ordering. We argue that similar mechanisms are at work in other compounds, and thus present a unifying framework to understand CMR in seemingly different materials.