Factors affecting the optimal design of high-Tc superconductors — the pseudogap and critical doping

Abstract The impact of the normal-state pseudogap, present in all optimal and underdoped HTS cuprates, on critical currents and critical temperature is surveyed. With the opening of the pseudogap around a doping state of p ≈0.19 the condensation energy and superfluid density are rapidly suppressed due to reduction in the normal-state spectral weight. Even by optimal doping ( p ≈0.16) these measures of the ‘strength’ of superconductivity are diminished by up to 40%. This results in a sharp reduction in critical currents and irreversibility field, respectively. The optimal doping state where these properties are maximised is therefore not at maximum T c but in the lightly overdoped region where the pseudogap energy falls to zero at p ≈0.19. The presence of impurities and grain boundaries further heightens these effects.