Quantum fluctuations of charge order induce phonon softening in a superconducting cuprate

TL;DR

This study investigates quantum fluctuations of charge order in a cuprate superconductor, revealing phonon softening and quantum critical behavior near optimal doping, which advances understanding of high-temperature superconductivity.

Contribution

It provides experimental evidence of charge order fluctuations and their impact on phonons, highlighting quantum critical phenomena in LSCO.

Findings

Short-range charge orders observed near optimal doping.

Phonon branches significantly soften due to charge correlations.

Evidence of quantum critical scaling and discommensurations.

Abstract

Quantum phase transitions play an important role in shaping the phase diagram of high-temperature cuprate superconductors. These cuprates possess intertwined orders which interact strongly with superconductivity. However, the evidence for the quantum critical point associated with the charge order in the superconducting phase remains elusive. Here we show the short-range charge orders and the spectral signature of the quantum fluctuations in La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) near the optimal doping using high-resolution resonant inelastic X-ray scattering. On performing calculations through a diagrammatic framework, we discovered that the charge correlations significantly soften several branches of phonons. These results elucidate the role of charge order in the LSCO compound, providing evidence for quantum critical scaling and discommensurations associated with charge order.