近日，复旦大学的张成&修发贤及其研究团队与华东师范大学的袁翔等人合作并取得一项新进展。经过不懈努力，他们在CaAs₃中的Mott-Ioffe-Regel极限附近观察到量子振荡。相关研究成果已于2024年3月29日在国际知名学术期刊《国家科学评论》上发表。

本文报道了在CaAs₃中Mott-Ioffe-Regel极限附近朗道量子化观测到的量子振荡。尽管CaAs₃的电阻率具有绝缘体般的温度依赖性，但它在费米表面表现出巨大的磁阻和突出的Shubnikov-de Haas振荡，表明其具有高相干带输运。相反，在磁转矩中不存在量子振荡。准粒子的有效质量随磁场的增大而系统地增大，比磁红外光谱给出的期望值大得多。这表明费米表面附近存在很强的多体重整化效应。研究人员发现这些非常规的行为可以用迁移率边缘和van Hove奇点之间的相互作用来解释，这导致了在扩散界出现的相干回旋加速器轨道的形成。这项研究结果需要进一步研究范霍夫奇点的电子关联效应。

据悉，Mott-Ioffe-Regel极限设定了相干准粒子输运的载流子平均自由程的下界。超过这个极限的金属丰度引起了极大的兴趣，因为它通常与量子临界性和非常规超导性密切相关。这一方向的研究进展主要集中在准粒子散射速率的演化过程中产生的奇异金属行为，如线性温度电阻率，而由于扩散界的平均自由程较短，对准粒子相干现象的研究较少。

附：英文原文

Title: Observation of quantum oscillations near the Mott-Ioffe-Regel limit in CaAs₃

Author: Wang, Yuxiang, Zhao, Minhao, Zhang, Jinglei, Wu, Wenbin, Li, Shichao, Zhang, Yong, Jiang, Wenxiang, Joseph, Nesta Benno, Xu, Liangcai, Mou, Yicheng, Yang, Yunkun, Leng, Pengliang, Zhang, Yong, Pi, Li, Suslov, Alexey, Ozerov, Mykhaylo, Wyzula, Jan, Orlita, Milan, Zhu, Fengfeng, Zhang, Yi, Kou, Xufeng, Zhu, Zengwei, Narayan, Awadhesh, Qian, Dong, Wen, Jinsheng, Yuan, Xiang, Xiu, Faxian, Zhang, Cheng

Issue&Volume: 2024-03-29

Abstract: The Mott-Ioffe-Regel limit sets the lower bound of carrier mean free path for coherent quasiparticle transport. Metallicity beyond this limit is of great interest because it is often closely related to quantum criticality and unconventional superconductivity. Progress along this direction mainly focuses on the strange-metal behaviors originating from the evolution of quasiparticle scattering rate such as linear-in-temperature resistivity, while the quasiparticle coherence phenomena in this regime are much less explored due to the short mean free path at the diffusive bound. Here we report the observation of quantum oscillations from Landau quantization near the Mott-Ioffe-Regel limit in CaAs₃. Despite the insulator-like temperature dependence of resistivity, CaAs3 presents giant magnetoresistance and prominent Shubnikov–de Haas oscillations from Fermi surfaces, indicating highly-coherent band transport. In contrast, the quantum oscillation is absent in the magnetic torque. The quasiparticle effective mass increases systematically with magnetic fields, manifesting a much larger value than the expectation given by magneto-infrared spectroscopy. It suggests a strong many-body renormalization effect near Fermi surface. We find that these unconventional behaviors may be explained by the interplay between the mobility edge and the van Hove singularity, which results in the formation of coherent cyclotron orbits emerging at the diffusive bound. Our results call for further study on the electron correlation effect of the van Hove singularity.

DOI: 10.1093/nsr/nwae127

Source: https://academic.oup.com/nsr/advance-article/doi/10.1093/nsr/nwae127/7637791