Magnetic polarons can generate colossal magnetoresistance in magnetic semiconductors, yet their terahertz electrodynamics remain largely unexplored. Here we report magneto-terahertz spectroscopy of the Eu-based Zintl antiferromagnet EuZn2P2. The low-frequency conductivity shows pronounced non-Drude behavior consistent with an evolution from isolated to overlapping magnetic polarons upon cooling. The polaron relaxation time reaches a maximum at the N\'eel temperature and exhibits a strong magnetic-field dependence. This polaron-driven reshaping of the conductivity leads to a strongly frequency-dependent magnetoresistance that becomes colossal in the terahertz range, reaching about 90 % at 1.5 THz, roughly three times larger than the zero-frequency limit value. These results demonstrate that magnetic polarons strongly govern the low-energy electrodynamics and highlight the sensitivity of terahertz spectroscopy to polaronic magnetotransport in correlated magnetic semiconductors.
@article{arxiv.2603.21423,
title = {Colossal Terahertz Magnetoresistance from Magnetic Polarons in EuZn$_2$P$_2$},
author = {E. Marulanda and M. Dutra and N. M. Kawahala and E. D. Stefanato and G. G. Vasques and J. Munevar and M. A. Avila and F. G. G. Hernandez},
journal= {arXiv preprint arXiv:2603.21423},
year = {2026}
}