Ubiquitous Charge Order Correlations in High-Temperature Superconducting Cuprates
The presence of charge order in high-transition-temperature copper oxides (high-Tc cuprates) was identified a decade ago. Now it is a universally observed order like the antiferromagnetic and the superconducting orders of the cuprates. The charge order shows up in various forms depending on materials, and it overlaps other orders in the phase diagram. Because of this diversity and complexity it has been far from clear whether or not the charge order has a direct relevance to superconductivity and to the mysterious pseudogap phenomenon. However, the research development in the last few years has been successful in revealing universal aspects of the charge order and its fluctuations. It turns out that the charge order is compatible with superconductivity, and that its fluctuations have high onset temperature and high energy scale comparable to those of the pseudogap. The charge order correlations might be indispensable for creating the pseudogap and possibly generating high-Tc superconductivity by collaborating with spin and pairing correlations.