Colossal Terahertz Magnetoresistance from Magnetic Polarons in EuZn$_2$P$_2$

TL;DR

This study reveals that magnetic polarons in EuZn₂P₂ cause colossal terahertz-range magnetoresistance, with terahertz spectroscopy uncovering their significant role in low-energy electrodynamics and magnetotransport.

Contribution

It provides the first detailed terahertz spectroscopic analysis of magnetic polarons in EuZn₂P₂, demonstrating their impact on colossal magnetoresistance at terahertz frequencies.

Findings

Magnetic polarons cause non-Drude conductivity behavior.

Polaron relaxation time peaks at the Néel temperature.

Magnetoresistance reaches about 90% at 1.5 THz.

Abstract

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 EuZn$_2$P$_2$. 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.