Possible origin of 60-K plateau in the YBa2Cu3O(6+y) phase diagram

TL;DR

This study uses a semi-microscopic XY model to explore the origins of the 60-K plateau in YBa2Cu3O(6+y), suggesting that charge imbalance and doping effects, rather than oxygen ordering alone, contribute to this feature.

Contribution

The paper introduces a three-dimensional XY model with anisotropic parameters to analyze the YBCO phase diagram and proposes a new explanation for the 60-K plateau involving charge imbalance effects.

Findings

Oxygen ordering alone unlikely causes the 60-K plateau.

Charge imbalance between CuO2 planes and other sites influences Tc.

Doping effects lead to competing factors that may produce the plateau.

Abstract

We study a model of YBa2Cu3O(6+y) to investigate the influence of oxygen ordering and doping imbalance on the critical temperature Tc(y) and to elucidate a possible origin of well-known feature of YBCO phase diagram: the 60-K plateau. Focusing on "phase only" description of the high-temperature superconducting system in terms of collective variables we utilize a three-dimensional semi microscopic XY model with two-component vectors that involve phase variables and adjustable parameters representing microscopic phase stiffnesses. The model captures characteristic energy scales present in YBCO and allows for strong anisotropy within basal planes to simulate oxygen ordering. Applying spherical closure relation we have solved the phase XY model with the help of transfer matrix method and calculated Tc for chosen system parameters. Furthermore, we investigate the influence of oxygen ordering and doping imbalance on the shape of YBCO phase diagram. We find it unlikely that oxygen ordering alone can be responsible for the existence of 60-K plateau. Relying on experimental data unveiling that oxygen doping of YBCO may introduce significant charge imbalance between CuO2 planes and other sites, we show that simultaneously the former are underdoped, while the latter -- strongly overdoped almost in the whole region of oxygen doping in which YBCO is superconducting. As a result, while oxygen content is increased, this provides two counter acting factors, which possibly lead to rise of 60K plateau. Additionally, our result can provide an important contribution to understanding of experimental data supporting existence of multicomponent superconductivity in YBCO.