Non-monotonic electron interactions in the copper oxide plane

In strongly correlated systems the strength of Coulomb interactions between electrons plays a central role in determining their emergent quantum mechanical phases. Specifically, while electrons in free space have a Coulomb interaction energy that decays monotonically with distance, in solids, where the electrons move in a polarizable crystal, the effective Coulomb interaction may be non-monotonic, with a minimum at a finite length. This general concept of how electrons in solids interact may be key to understanding the emerging electronic phases of strongly correlated quantum materials. For instance, a non-monotonic behavior may result in an attractive interaction that could lead to superconductivity or density wave order.
We performed resonant x-ray scattering on Bi2Sr2CaCuO8+x, a prototypical cuprate superconductor, to probe electronic correlations within the CuO2 plane. We discovered a dynamic quasi-circular pattern in the x-y scattering plane with a wave vector radius that is determined by the minimum of the Coulomb potential [1]. Furthermore, this radius exactly matches the wave vector magnitude of the well-known static charge order patterns. Along with a comprehensive set of doping- and temperature-dependent measurements, our experiments reveal a picture of charge order competing with superconductivity where short-range domains along x and y are allowed to dynamically rotate into any other in-plane direction [1].

[1] Boschini et al. Nature Communications 12, 597 (2021)