Spectroscopic Evidence for Charge Order Melting via Quantum Fluctuations in a Cuprate

TL;DR

This study uses resonant inelastic x-ray scattering to provide spectroscopic evidence of quantum fluctuations causing charge order melting in a cuprate superconductor, highlighting the role of quantum criticality.

Contribution

It reveals spectroscopic signatures of quantum fluctuations associated with charge order in a cuprate, linking them to quantum critical behavior near superconductivity.

Findings

Charge order fluctuations increase with decreasing temperature.

Fano-like interference indicates strong coupling between charge order fluctuations and phonons.

Quantum critical fluctuations lead to charge order melting near optimal doping.

Abstract

Copper-oxide high TC superconductors possess a number of exotic orders co-existing with or proximal to superconductivity, whose quantum fluctuations may account for the unusual behaviors of the normal state, even affecting superconductivity. Yet, spectroscopic evidence about such quantum fluctuations remains elusive. Here, we reveal spectroscopic fingerprints for such fluctuations associated with a charge order (CO) in nearly optimally-doped Bi2Sr2CaCu2O8+d, using resonant inelastic x-ray scattering (RIXS). In the superconducting state, while the quasi-elastic CO signal decreases with temperature, the interplay between CO fluctuations and bond-stretching phonons in the form of a Fano-like interference paradoxically increases, incompatible with expectations for competing orders. Invoking general principles, we argue that this behavior reflects the properties of a dissipative system near an order-disorder quantum critical point, where the dissipation varies with the opening of the pseudogap and superconducting gap at low temperatures, leading to the proliferation of quantum critical fluctuations which melt CO.