Hole doping dependence of critical current density in YBa2Cu3O7−δ conductors

Abstract

One of the central themes in cuprate superconductivity is the evolution of the electronic properties with the charge carrier concentration, p, expressed as the number of holes per Cu ion in the CuO2 planes. In YBa2Cu3O7−δ (YBCO), p is well known to vary with oxygen content (δ) and with substitution of Ca2+ for Y3+. In this Letter, we show that p also varies with the fraction of Cu–O “chain layer” stacking faults. The resulting parabolic variation in the superconducting transition temperature (Tc) is also well known; however, the effect on the critical current density (Jc) is less well explored. We show that the self-field Jc follows a common trend for all these hole doping methods, rising to a sharp peak on the slightly overdoped side of the Tc(p) parabola. In contrast, the in-field Jc anisotropy at high temperatures and low fields is determined solely by the stacking-fault fraction, not by hole doping, such that a sample free from stacking faults tends towards an isotropic Jc. These results serve to emphasize the role of sample microstructure in determining Jc in-field anisotropy.