Recent experiments suggest a new paradigm towards novel colossal magnetoresistance (CMR) in a family of materials EuM2X2(M=Cd, In, Zn; X=P, As), distinct from the traditional avenues involving Kondo-RKKY crossovers, magnetic phase transitions with structural distortions, or topological phase transitions. Here, we use angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations to explore their origin, particularly focusing on EuCd2P2. While the low-energy spectral weight royally tracks that of the resistivity anomaly near the temperature with maximum magnetoresistance (TMR) as expected from transport-spectroscopy correspondence, the spectra are completely incoherent and strongly suppressed with no hint of a Landau quasiparticle. Using systematic material and temperature dependence investigation complemented by theory, we attribute this non-quasiparticle caricature to the strong presence of entangled magnetic and lattice interactions, a characteristic enabled by the p-f mixing. Given the known presence of ferromagnetic clusters, this naturally points to the origin of CMR being the scattering of spin-polarized polarons at the boundaries of ferromagnetic clusters. These results are not only illuminating to investigate the strong correlations and topology in EuCd2X2 family, but, in a broader view, exemplify how multiple cooperative interactions can give rise to extraordinary behaviors in condensed matter systems.
@article{arxiv.2410.22727,
title = {Colossal magnetoresistance from spin-polarized polarons in an Ising system},
author = {Ying-Fei Li and Emily M. Been and Sudhaman Balguri and Chun-Jing Jia and Mira B. Mahenderu and Zhi-Cheng Wang and Yi Cui and Su-Di Chen and Makoto Hashimoto and Dong-Hui Lu and Brian Moritz and Jan Zaanen and Fazel Tafti and Thomas P. Devereaux and Zhi-Xun Shen},
journal= {arXiv preprint arXiv:2410.22727},
year = {2025}
}