[论文解读] Materials and possible mechanisms of extremely large magnetoresistance: A review

Niu, Rui, Zhu, W. K.|arXiv (Cornell University)|Oct 20, 2021

Chemical and Physical Properties of Materials被引用 46

一句话总结

本综述综合了当前对金属和半金属中极端大磁阻（XMR）的理解，识别出电子-空穴补偿和高载流子迁移率作为主要机制。文章强调了拓扑半金属——尤其是外尔和狄拉克材料（如WTe2和TaAs）——在实现超过10^8%且在高磁场下仍不饱和的XMR值中的关键作用，为低功耗自旋电子学和量子器件提供了潜在应用前景。

ABSTRACT

Magnetoresistance (MR) is a characteristic that the resistance of a substance changes with the external magnetic field, reflecting various physical origins and microstructures of the substance. A large MR, namely a huge response to a low external field, has always been a useful functional feature in industrial technology and a core goal pursued by physicists and materials scientists. Conventional large MR materials are mainly manganites, whose colossal MR (CMR) can be as high as -90%. The dominant mechanism is attributed to spin configuration aligned by the external field, which reduces magnetic scattering and thus resistance. In recent years, some new systems have shown an extremely large unsaturated MR (XMR). Unlike ordinary metals, the positive MR of these systems can reach 103-108% and is persistent under super high magnetic fields. The XMR materials are mainly metals or semimetals, distributed in high-mobility topological or non-topological systems, and some are magnetic, which suggests a wide range of application scenarios. Various mechanisms have been proposed for the potential physical origin of XMR, including electron-hole compensation, steep band, ultrahigh mobility, high residual resistance ratio, topological fermions, etc. It turns out that some mechanisms play a leading role in certain systems, while more are far from clearly defined. In addition, the researches on XMR are largely overlapped or closely correlated with other recently rising physics and materials researches, such as topological matters and two-dimensional (2D) materials, which makes elucidating the mechanism of XMR even more important. Moreover, the disclosed novel properties will lay a broad and solid foundation for the design and development of functional devices. In this review, we will discuss several aspects in the following order: ...

研究动机与目标

• 系统综述极端大磁阻（XMR）的材料基础与物理机制。
• 阐明电子-空穴补偿、高迁移率及拓扑能带结构在实现XMR中的作用。
• 探讨XMR与二维材料和拓扑量子物质等新兴领域之间的相互作用。
• 识别当前挑战与未来研究方向，以推动实际器件集成。

提出的方法

• 按化学组成对XMR材料进行系统分类：元素、二元化合物（如XP、XBi、TMDs）和三元化合物（如ZrSiS、Co3Sn2S2）。
• 分析实验输运数据，包括纵向和横向磁阻、角度依赖性以及量子振荡。
• 利用角分辨光电子能谱（ARPES）和扫描隧道显微光谱探测电子结构和费米弧。
• 通过理论建模能带结构，包括外尔点和节点线，将拓扑性质与XMR相关联。
• 比较不同残余电阻率比（RRR）、载流子浓度和有效质量的材料中XMR行为的差异。
• 通过负纵向磁阻作为拓扑外尔半金属的特征，评估手征异常效应。

实验结果

研究问题

• RQ1 非磁性金属和半金属中极端且不饱和磁阻的物理机制是什么？
• RQ2 为何某些拓扑半金属（如WTe2和TaAs）的XMR值可超过10^8%且不发生饱和？
• RQ3 电子-空穴补偿与高载流子迁移率如何协同促进XMR？
• RQ4 二维和范德华异质结构在多大程度上改变XMR行为？
• RQ5 为何石墨烯尽管具有高迁移率和狄拉克费米子，却仅表现出约200%的磁阻？

主要发现

• 在WP2中，于2.5 K和63 T条件下观测到高达2 × 10^8%的XMR，归因于电子-空穴补偿、高迁移率以及极高的残余电阻率比（RRR）。
• WTe2在高达60 T的磁场下表现出不饱和XMR，负纵向磁阻证实了其通过手征异常表现出的II型外尔半金属特性。
• ARPES测量证实Co3Sn2S2中存在线性能带色散和费米弧，支持其作为磁性外尔半金属的分类。
• ZrSiS和ZrSiSe表现出超高迁移率和量子振荡，表明存在狄拉克型准粒子并具有XMR潜力。
• 层状材料如WTe2和Cd3As2纳米片的XMR具有显著的厚度依赖性，表明存在量子限制效应。
• 尽管具有高迁移率和狄拉克特征，石墨烯仅表现出约200%的磁阻，表明带结构细节或散射机制等额外因素限制了该体系中的XMR。