Anisotropic Fano resonance in the Weyl semimetal candidate LaAlSi
Anisotropic Fano resonance in the Weyl semimetal candidate LaAlSi
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DOI：
10.1103/physrevb.102.235162
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发表时间：
2020-12
影响因子：
3.7
通讯作者：
Kunyan Zhang;Tong Wang;Xiaoqi Pang;Fei Han;S. Shang;N. T. Hung;Zi-kui Liu;Mingda Li;R. Saito;Shengxi Huang
中科院分区：
文献类型：
--
作者：
Kunyan Zhang;Tong Wang;Xiaoqi Pang;Fei Han;S. Shang;N. T. Hung;Zi-kui Liu;Mingda Li;R. Saito;Shengxi Huang
拓扑Weyl半金属(WSM)是手性Weyl费米子的固态实现，其声子行为提供了对其电子性质的深入了解。在这项工作中，利用偏振拉曼光谱观察到了第二类WSM候选材料LaAlSi中的各向异性Fano共振。只有在488和532 nm激光激发下，LaAlSi的声子模才出现不对称线形，而在364、633和785 nm激发下不出现，这表明了激发的选择性。在偏振拉曼光谱中，声子模的不对称性、频率和线宽以及光谱背景都表现出随偏振角的四重旋转对称性。金属或半金属中的拉曼频移通常归因于Kohn反常，而LaAlSi中的各向异性频移不能用Kohn反常效应来解释，而潜在地可以用Fano共振的各向异性散射背景来解释。用第一性原理计算了电子能带结构和声子色散，讨论了Fano共振的激发能量依赖性和各向异性行为的起源。
Topological Weyl semimetal (WSM) is a solid-state realization of chiral Weyl fermions, whose phonon behaviors provide in-depth knowledge of their electronic properties. In this work, anisotropic Fano resonance is observed in a type-II WSM candidate LaAlSi by polarized Raman spectroscopy. The asymmetric line shape occurs for the ${B}_{1}^{2}$ phonon mode of LaAlSi only for 488- and 532-nm laser excitations but not for 364-, 633-, and 785-nm excitations, suggesting the excitation selectivity. The asymmetry, frequency, and linewidth of the ${B}_{1}^{2}$ phonon mode, along with the spectral background, all show fourfold rotational symmetry as a function of the polarization angle in the polarized Raman spectra. While the shift of Raman frequency in a metal or semimetal is typically attributed to Kohn anomaly, here we show that the anisotropic frequency shift in LaAlSi cannot be explained by the effect of Kohn anomaly, but potentially by the anisotropic scattering background of Fano resonance. Origins of the excitation-energy dependence and anisotropic behavior of the Fano resonance are discussed by the first-principles calculated electronic band structure and phonon dispersion.