Charge order at high temperature in cuprate superconductors

TL;DR

Recent resonant X-ray scattering studies reveal that high-temperature charge modulations in cuprate superconductors are widespread, persist above the pseudogap temperature, and are dynamically coupled to lattice and magnetic excitations, challenging previous low-temperature confined views.

Contribution

This review highlights the discovery of high-temperature charge density wave modulations in cuprates, emphasizing their extended presence and dynamic properties across different families.

Findings

Charge modulations exist at temperatures well above the pseudogap.

High-temperature charge order coexists with low-temperature CDW.

Dynamical coupling of charge order to lattice and magnetic excitations is observed.

Abstract

The presence of different electronic orders other than superconductivity populating the phase diagram of cuprates suggests that they might be the key to disclose the mysteries of this class of materials. In particular charge order in the form of charge density waves (CDW), i.e., the incommensurate modulation of electron density in the CuO$_2$ planes, is ubiquitous across different families and presents a clear interplay with superconductivity. Until recently, CDW had been found to be confined inside a rather small region of the phase diagram, below the pseudogap temperature and the optimal doping. This occurrence might shed doubts on the possibility that such "low temperature phenomenon" actually rules the properties of cuprates either in the normal or in the superconducting states. However, recent resonant X-ray scattering (RXS) experiments are overturning this paradigm. It results that very short-ranged charge modulations permeate a much wider region of the phase diagram, coexisting with CDW at lower temperatures and persisting up to temperatures well above the pseudogap opening. Here we review the characteristics of these high temperature charge modulations, which are present in several cuprate families, with similarities and differences. A particular emphasis is put on their dynamical character and on their coupling to lattice and magnetic excitations, properties that can be determined with high resolution resonant inelastic x-ray scattering (RIXS).