Probing electronic order via coupling to low energy phonons in superconducting Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+\delta}$

TL;DR

This study uses high-resolution inelastic x-ray scattering to investigate phonon behavior in cuprate superconductors, revealing coupling to electronic density waves and symmetry breaking that intensify in the pseudogap state.

Contribution

It provides direct evidence of phonon anomalies linked to electronic order and symmetry breaking in a cuprate superconductor, advancing understanding of pseudogap phenomena.

Findings

Anomalous broadening of longitudinal acoustic phonons near (1/4,1/4,0)

Coupling of phonons to electronic density wave state

Broken time-reversal and inversion symmetries in the pseudogap state

Abstract

We report high-resolution inelastic x-ray scattering measurements of the acoustic phonons in the single-layer cuprate $Bi_{2}Sr_{2-x)La_{x}CuO_{6+\delta}$. These measurements reveal anomalous broadening of the longitudinal acoustic phonon near the (1/4,1/4,0) wavevector. The observed wavevector and its doping dependence indicate the coupling of the phonons to an underlying electronic density wave state. In addition, a comparison of the scattered intensities for x-ray energy-gain and x-ray energy-loss indicates that both time-reversal and inversion symmetries are broken in the material. Upon cooling, the effects of symmetry breaking are enhanced in the pseudogap state.