Momentum-dependent charge correlations in YBa$_2$Cu$_3$O$_{6+\delta}$ superconductors probed by resonant x-ray scattering: Evidence for three competing phases

TL;DR

This study uses resonant x-ray scattering to explore charge correlations in YBa2Cu3O6+δ superconductors, revealing three competing phases involving charge density waves, magnetic order, and superconductivity, influenced by doping and external magnetic fields.

Contribution

It provides new insights into the momentum-dependent charge correlations and the interplay of three competing phases in underdoped YBa2Cu3O6+δ superconductors.

Findings

Nearly critical biaxial charge density wave correlations at specific wave vectors.

Enhanced CDW amplitude and correlation length under magnetic fields weakening superconductivity.

Reduced CDW features in crystals with Zn impurities indicating competition with magnetic order.

Abstract

We have used resonant x-ray scattering to determine the momentum dependent charge correlations in YBa$_2$Cu$_3$O$_{6.55}$ samples with highly ordered chain arrays of oxygen acceptors (ortho-II structure). The results reveal nearly critical, biaxial charge density wave (CDW) correlations at in-plane wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length are enhanced as superconductivity is weakened by an external magnetic field. Analogous experiments were carried out on a YBa$_2$Cu$_3$O$_{6.6}$ crystal with a dilute concentration of spinless (Zn) impurities, which had earlier been shown to nucleate incommensurate magnetic order. Compared to pristine crystals with the same doping level, the CDW amplitude and correlation length were found to be strongly reduced. These results indicate a three-phase competition between spin-modulated, charge-modulated, and superconducting states in underdoped YBa$_2$Cu$_3$O$_{6+\delta}$.