Topological Singularity Induced Chiral Kohn Anomaly in a Weyl Semimetal

Abstract

The electron-phonon interaction (EPI) is instrumental in a wide variety of phenomena in solid-state physics, such as electrical resistivity in metals, carrier mobility, optical transition, and polaron effects in semiconductors, lifetime of hot carriers, transition temperature in BCS superconductors, and even spin relaxation in diamond nitrogen-vacancy centers for quantum information processing. However, due to the weak EPI strength, most phenomena have focused on electronic properties rather than on phonon properties. One prominent exception is the Kohn anomaly, where phonon softening can emerge when the phonon wave vector nests the Fermi surface of metals. Here we report a new class of Kohn anomaly in a topological Weyl semimetal (WSM), predicted by field-theoretical calculations, and experimentally observed through inelastic x-ray and neutron scattering on WSM tantalum phosphide. Compared to the conventional Kohn anomaly, the Fermi surface in a WSM exhibits multiple topological singularities of Weyl nodes, leading to a distinct nesting condition with chiral selection, a power-law divergence, and nonnegligible dynamical effects. Our work brings the concept of the Kohn anomaly into WSMs and sheds light on elucidating the EPI mechanism in emergent topological materials.

Anisotropic Fano resonance in the Weyl semimetal candidate LaAlSi

“…It is noted that the phonon in LaAlSi can couple to free carriers by electron-phonon interaction, but the electron-phonon interaction known as the Kohn anomaly does not give rise to the angle dependence of phonon frequency. Kohn anomaly is the origin of the frequency modulation of a metal or semimetal, in which the phonon frequency is renormalized by excitation of an electron-hole pair near the Fermi energy by the electron-phonon interaction [42,43]. Since the electronic structure of LaAlSi can potentially host Weyl-nodes-like features near the Fermi energy, the Kohn anomaly effect is possible to occur at phonon wave vector q ≈ 0.…”

“…Transport measurements including resistivity and Hall effect were performed on the Quantum Design Physical Property Measurement System. Resistivity and Hall effect measurements were simultaneously carried out on a rectangle crystal using a five-probe geometry [42,43]. The current is along the a or b axes (a and b are equivalent) and the magnetic fields were applied along the c axis.…”

Phonon-limited Transport and Fermi Arc Lifetime in Weyl Semimetals

“…While we investigate phonon-induced effects on the electronic properties of WSMs, it is also of significant interest to study electron-induced effects on phonon observables. For instance, recent works have addressed the Kohn anomaly [78][79][80] and quantum oscillations of the sound velocity [81,82] in WSMs. Future theoretical work could study such phenomena using the framework presented below.…”

Phonon-induced magnetoresistivity of Weyl semimetal nanowires

“…The importance of phonons in WSMs has been established by recent experiments [16][17][18][19]. Phonon effects can be identified, for instance, through the characteristic temperature dependence of phonon-induced contributions to transport observables.…”