Anisotropic Fano resonance in the Weyl semimetal candidate LaAlSi

Abstract

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 2 1 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 2 1 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.

Electron–Phonon and Spin–Lattice Coupling in Atomically Thin Layers of MnBi2Te4

“…Fano line shape is often attributed to electron−phonon interaction. 27,38 Concurrent with the changes of the Fano parameter as a function of temperature, we also observe that the line width and the integrated intensity of the A 1g (1) mode in the 4-and 5-SLs evolve in a qualitatively similar way (Figure 3c). The temperature dependence of both the line widths and intensity are well-described by the anharmonic decay model.…”

“…In the insulating phase, electron–phonon scattering is reduced as the gap impedes phonon-mediated electron transitions, which is manifested in the reduced Fano parameter below the Néel temperature in both 4- and 5-SL samples as shown in Figure b. Fano line shape is often attributed to electron–phonon interaction. , …”

Observation of Fermi arcs and Weyl nodes in a non-centrosymmetric magnetic Weyl semimetal

“…Recently, the RAlGe and RAlSi (R = Rare earth elements) materials, which are noncentrosymmetric, have been proposed as a new family of magnetic WSMs, where the Weyl nodes are tunable due to intrinsic magnetic order [24][25][26][27][28][29][30]. These families of compounds can exhibit different types of magnetic ground states and host Type-I or Type-II Weyl fermions.…”

Laser‐induced Fano interference subsumed by electron–phonon coupling in orthorhombic KNbO3nano‐bricks: An ab initio vibrational and Raman spectroscopic investigation

“…Its sluggish rising trend can be noted from Figure 6E. Miscellaneous local mechanisms such as lattice disorder, crystal field effects, material‐specific anisotropic deviations, commensurate or incommensurate interaction of phonons with spins, charge carriers and surrounding phonons can lead to phonon damping 57–59 . Electron–phonon coupling has a general tendency of renormalizing the peak‐wavenumbers that supports the functional form of Einstein's approximation for gap renormalization 20 .…”