近日，美国斯坦福直线加速器中心国家加速器实验室的Zhi-Xun Shen&Ying-Fei Li及其研究团队取得一项新进展。他们对源于伊辛系统中自旋极化极化子的庞磁电阻进行了研究。相关研究成果已于2024年12月2日在国际知名学术期刊《美国科学院院刊》上发表。

该研究团队利用角分辨光发射谱和密度泛函理论计算来探究其起源，特别聚焦于EuCd₂P₂。虽然低能谱权重如预期般随着电阻率异常在最大磁阻（TMR）温度附近的变化而变化，符合输运-光谱对应关系，但光谱却完全不相干且受到强烈抑制，没有朗道准粒子的迹象。

通过结合理论的系统性材料和温度依赖性研究，研究人员将这种非准粒子特征归因于强磁与晶格相互作用的共存，这是由p-f混合所赋予的特性。鉴于已知存在铁磁团簇，这自然指向了CMR的起源：自旋极化极化子在铁磁团簇边界的散射。这些结果不仅为探究EuCd₂X₂家族中的强关联和拓扑性质提供了启示，而且从更广泛的角度来看，也例证了多种协同相互作用如何在凝聚态系统中产生非凡行为。

据悉，最近的实验提出一种新范式，在EuM₂X₂（M = Cd、In、Zn；X = P、As）这一系列材料中实现新型庞磁电阻（CMR），这种新范式有别于传统的Kondo–Ruderman–Kittel–Kasuya–Yosida交叉、伴随结构扭曲的磁相变或拓扑相变等途径。

附：英文原文

Title: Colossal magnetoresistance from spin-polarized polarons in an Ising system

Author: Li, Ying-Fei, Been, Emily M., Balguri, Sudhaman, Jia, Chun-Jing, Mahendru, Mira B., Wang, Zhi-Cheng, Cui, Yi, Chen, Su-Di, Hashimoto, Makoto, Lu, Dong-Hui, Moritz, Brian, Zaanen, Jan, Tafti, Fazel, Devereaux, Thomas P., Shen, Zhi-Xun

Issue&Volume: 2024-12-2

Abstract: Recent experiments suggest a new paradigm toward novel colossal magnetoresistance (CMR) in a family of materials EuM₂X₂ (M = Cd, In, Zn; X = P, As), distinct from the traditional avenues involving Kondo–Ruderman–Kittel–Kasuya–Yosida crossovers, magnetic phase transitions with structural distortions, or topological phase transitions. Here, we use angle-resolved photoemission spectroscopy and density functional theory 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 (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 nonquasiparticle 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.

DOI: 10.1073/pnas.2409846121

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2409846121