[论文解读] Hall anomaly, Quantum Oscillations and Possible Lifshitz Transitions in Kondo Insulator YbB$_{12}$: Evidence for Unconventional Charge Transport

Ziji Xiang, Kuan-Wen Chen+11 more|arXiv (Cornell University)|Nov 17, 2021

Rare-earth and actinide compounds被引用 9

一句话总结

本研究通过高场输运测量与扭矩磁力仪，揭示了重费米子绝缘体YbB12中非传统的电荷输运行为，识别出霍尔异常、量子振荡以及在19.6 T和~31 T处的场诱导利什蒂茨相变。数据支持一种双流体模型，其中电荷中性准粒子与非金属电荷载流子共存，朗道能级量化与散射作用使Shubnikov-de Haas效应可观测，暗示一种新型量子物相的存在。

ABSTRACT

In correlated electronic systems, strong interactions and the interplay between different degrees of freedom may give rise to anomalous charge transport properties, which can be tuned by external parameters like temperature and magnetic field. Recently, magnetic quantum oscillations and metallic low-temperature thermal conductivity have been observed in the Kondo insulator YbB$_{12}$, whose resistivity is a few orders of magnitude higher than those of conventional metals. As yet, these unusual observations are not fully understood. Here we present a detailed investigation of the behavior of YbB$_{12}$ under intense magnetic fields using both transport and torque magnetometry measurements. A low-field Hall anomaly, reminiscent of the Hall response associated with "strange-metal" physics, develops at $T < 1.5$ K. At two characteristic magnetic fields ($μ_0H_1= 19.6$ T and $μ_0H_2 \sim 31$ T), signatures appear in the Hall coefficient, magnetic torque, and magnetoresistance. We suggest that they are likely to be field-induced Lifshitz transitions. Moreover, above 35 T, the background resistivity displays an unusual, nonmetallic $T^α$-behavior, with $α$ being field-dependent and varying between -1.5 and -2. By normalizing the Shubnikov-de Haas oscillation amplitude to this $T^α$-dependence, the calculated cyclotron mass becomes more consistent with that deduced from de Haas-van Alphen oscillations. Our results support a novel two-fluid scenario in YbB$_{12}$: a Fermi-liquid-like fluid of charge-neutral quasiparticles coexists with charge carriers that remain in a nonmetallic state. The former experience successive Lifshitz transitions and develop Landau quantization in applied magnetic fields, whilst scattering between both fluids allows the Shubnikov-de Haas effect to be observed in the electrical transport.

研究动机与目标

• 解决重费米子绝缘体YbB12中异常低温电阻率与金属态热导率的起源问题。
• 研究强磁场下霍尔异常与量子振荡的性质。
• 确定场诱导利什蒂茨相变是否可解释磁阻与振荡频率的变化。
• 检验包含共存费米液体类与非金属电荷载流子的双流体模型假设。
• 确立电子关联与杂化能隙物理在实现非传统输运中的作用。

提出的方法

• 在最高达35 T的磁场下，对YbB12单晶进行了高精度输运与扭矩磁力仪测量。
• 通过分析霍尔电阻率与磁阻，提取场依赖的霍尔系数与量子振荡频率。
• 对振荡分量进行快速傅里叶变换（FFT），以识别主导的量子振荡频率及其谐频。
• 将Shubnikov-de Haas振荡振幅归一化至非金属T^α背景电阻率，以提取一致的量子有效质量。
• 将电阻率的场依赖性建模为T^α，其中α介于-1.5至-2之间，表明非费米液体行为。
• 评估晶体电场（CEF）能级与塞曼分裂在场诱导能隙关闭及可能相变中的作用。

实验结果

研究问题

• RQ1 在T < 1.5 K时，YbB12中霍尔异常的成因是什么？为何其偏离标准双带德鲁德模型？
• RQ2 在μ₀H₁ = 19.6 T与μ₀H₂ ≈ 31 T处观测到的特征是否表明存在场诱导利什蒂茨相变？
• RQ3 Shubnikov-de Haas效应中的量子振荡如何与费米面及量子有效质量的变化相关？
• RQ4 具有场依赖α的非金属T^α电阻率背景的起源是什么？
• RQ5 电荷中性准粒子与非金属电荷载流子的共存是否可解释观测到的输运异常？

主要发现

• 霍尔电阻率表现出强烈的非线性场依赖性，与标准双带德鲁德模型不一致，表明存在非传统散射机制。
• 在T = 1.5 K以下出现低场霍尔异常，类似于奇异金属行为，暗示非费米液体物理。
• 在μ₀H₁ = 19.6 T与μ₀H₂ ≈ 31 T处，霍尔系数、磁扭矩与磁阻中出现显著特征，与量子振荡频率的变化同步。
• 量子振荡在35 T以上最为显著，主导频率F ≈ 670–680 T，FFT谱中清晰呈现高次谐频。
• 背景电阻率遵循非金属T^α依赖关系，其中α随磁场变化，范围为-1.5至-2，表明强电子关联效应。
• 将Shubnikov-de Haas振荡振幅归一化至T^α背景后，获得的量子有效质量与de Haas-van Alphen测量结果一致，支持双流体模型。