Colossal magnetoresistance from spin-polarized polarons in an Ising system

TL;DR

This study reveals that colossal magnetoresistance in EuCd$_2$P$_2$ arises from spin-polarized polarons scattering at ferromagnetic cluster boundaries, driven by strong magnetic and lattice interactions, as shown through ARPES and DFT analyses.

Contribution

It introduces a new paradigm for CMR involving spin-polarized polarons in an Ising system, distinct from traditional mechanisms, supported by combined experimental and theoretical evidence.

Findings

Spectral weight tracks resistivity anomaly near T$_{MR}$

Spectra are incoherent with no Landau quasiparticles

CMR originates from scattering of spin-polarized polarons at ferromagnetic cluster boundaries

Abstract

Recent experiments suggest a new paradigm towards novel colossal magnetoresistance (CMR) in a family of materials EuM$_2$X$_2$(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 EuCd$_2$P$_2$. While the low-energy spectral weight royally tracks that of the resistivity anomaly near the temperature with maximum magnetoresistance (T$_{MR}$) 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 EuCd$_2$X$_2$ family, but, in a broader view, exemplify how multiple cooperative interactions can give rise to extraordinary behaviors in condensed matter systems.