Observation of Raman active phonon with Fano lineshape in quasi-one-dimensional superconductor K$_2$Cr$_3$As$_3$

TL;DR

This study uses polarized Raman scattering to identify phonon modes in the quasi-one-dimensional superconductor K$_2$Cr$_3$As$_3$, revealing a Fano lineshape indicative of coupling between magnetic fluctuations and the lattice.

Contribution

First observation of a Fano lineshape in Raman-active phonons of K$_2$Cr$_3$As$_3$, linking magnetic fluctuations to lattice vibrations through first-principles calculations.

Findings

Detection of a Fano lineshape in one phonon mode

Identification of phonon modes consistent with calculations

Evidence of magnetic fluctuation coupling to lattice

Abstract

We performed a polarized Raman scattering study of quasi-one-dimensional superconductor K$_2$Cr$_3$As$_3$. We detect two A$_1^\prime$ phonons and three E$^\prime$ phonons. One of the A$_1^\prime$ modes exhibits a nearly temperature-independent Fano lineshape. Based on our first-principles calculations, we ascribe this mode to the in-phase vibrations of Cr atoms within one layer. This observation strongly suggests that the magnetic fluctuations in K$_2$Cr$_3$As$_3$ are coupled to the electronic structure \emph{via} the lattice.