Effective holographic theory of charge density waves

There are increasing indications that superconductivity competes with other orders in cuprate superconductors, but obtaining direct evidence with bulk-sensitive probes is challenging. We have used resonant soft x-ray scattering to identify two-dimensional charge fluctuations with an incommensurate periodicity of \(\bf \sim 3.2\) lattice units in the copper-oxide planes of the superconductors (Y,Nd)Ba\(_2\)Cu\(_3\)O\(_{6+x}\) with hole concentrations \(0.09 \leq p \leq 0.13\) per planar Cu ion. The intensity and correlation length of the fluctuation signal increase strongly upon cooling down to the superconducting transition temperature, \(T_c\); further cooling below \(T_c\) abruptly reverses the divergence of the charge correlations. In combination with prior observations of a large gap in the spin excitation spectrum, these data indicate an incipient charge-density-wave instability that competes with superconductivity.