Temperature-tunable Fano resonance induced by strong coupling between Weyl fermions and phonons in TaAs

TL;DR

This study demonstrates temperature-tunable Fano resonance in TaAs, caused by strong coupling between phonons and Weyl fermions, revealing insights into electron-phonon interactions in Weyl semimetals.

Contribution

It provides explicit evidence of strong phonon-Weyl fermion coupling and shows how Fano resonance can be tuned by temperature in TaAs.

Findings

Fano resonance observed in TaAs at low temperatures

Asymmetry diminishes with increasing temperature

Electronic transitions near Weyl points are suppressed at higher temperatures

Abstract

Strong coupling between discrete phonon and continuous electron-hole pair excitations can give rise to a pronounced asymmetry in the phonon line shape, known as the Fano resonance. This effect has been observed in a variety of systems, such as stripe-phase nickelates, graphene and high-$T_{c}$ superconductors. Here, we reveal explicit evidence for strong coupling between an infrared-active $A_1$ phonon and electronic transitions near the Weyl points (Weyl fermions) through the observation of a Fano resonance in the recently discovered Weyl semimetal TaAs. The resultant asymmetry in the phonon line shape, conspicuous at low temperatures, diminishes continuously as the temperature increases. This anomalous behavior originates from the suppression of the electronic transitions near the Weyl points due to the decreasing occupation of electronic states below the Fermi level ($E_{F}$) with increasing temperature, as well as Pauli blocking caused by thermally excited electrons above $E_{F}$. Our findings not only elucidate the underlying mechanism governing the tunable Fano resonance, but also open a new route for exploring exotic physical phenomena through the properties of phonons in Weyl semimetals.