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.

中文翻译：

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CaAs3 中莫特-约夫-雷格尔极限附近量子振荡的观察

Mott-Ioffe-Regel 极限设置了相干准粒子输运的载流子平均自由程的下限。超过这个极限的金属性引起了人们极大的兴趣，因为它通常与量子临界性和非常规超导性密切相关。沿着这个方向的进展主要集中在源自准粒子散射率演化的奇怪金属行为，例如线性温度电阻率，而由于在该状态下的平均自由程较短，因此对这一领域中的准粒子相干现象的探索要少得多。扩散界。在这里，我们报告了在 CaAs3 中莫特-约夫-雷格尔极限附近朗道量子化中观察到的量子振荡。尽管电阻率具有类似绝缘体的温度依赖性，但 CaAs3 呈现巨磁阻和来自费米表面的显着舒布尼科夫-德哈斯振荡，表明高度相干的带传输。相反，磁扭矩中不存在量子振荡。准粒子有效质量随磁场系统地增加，表现出比磁红外光谱给出的预期大得多的值。这表明费米表面附近存在强烈的多体重整化效应。我们发现这些非常规行为可以通过迁移率边缘和范霍夫奇点之间的相互作用来解释，这导致在扩散边界处出现相干回旋轨道的形成。我们的结果需要进一步研究范霍夫奇点的电子相关效应。