Correlation between Superfluid Density andTCof UnderdopedYBa2Cu3O6+x

Abstract

We report measurements of the ab-plane superfluid density ns (magnetic penetration depth, λ) of severely underdoped films of YBa2Cu3O6+x, with TCs from 6 to 50 K. TC is not proportional to ns(0); instead, we find TC ∝ n 1/2.3±0.4 s . At the lowest dopings, TC is as much as 5 times larger than the upper limit set by the KTB transition temperature of individual CuO2 bilayers.

An inhomogeneous Josephson phase in thin-film and high-Tc superconductors

“…Close to the metal-insulator transition the mean free path ℓ is of a small microscopic magnitude and it makes sense that the superconductor should be in the dirty limit (ℓ ≪ ξ 0 ). This implies [7] that the Homes law [6,7] (or the one reported by Zuev et al [8]) should then yield the valid correlation between n s and T c . The case of high-T c materials is further complicated due to the anisotropic gap and correlation length.…”

“…Finally, in 2005 Zuev et al [8] reported a linear relationship between n s and T χ c , where χ = 2.3 ± 0.4. They pointed out that with the empirical proportionality of T c to σ dc (theoretically justified in a classical Josephson-coupled superconductor [19]), the value of 2 for χ makes their result consistent with the one by Homes et al [6].…”

“…Here we review and strengthen the arguments of Ref. [1] and discuss their relevance to the intriguing n s -T c correlations [5,6,7,8].…”

“…In this paper we are interested in extending these ideas to give some insight into weak superconductivity in inhomogeneous systems, and thus whether we can understand data in films as well as in underdoped high-T c superconductors. In particular, we will present some insights on the Uemura correlation [5] and the "Homes law" [6,7] (see also [8]). …”

Large magnetic penetration depth and thermal fluctuations in a superconducting Ca10(Pt3As8)[(FeKim1, Ronning2, Haberkorn3 et al. 2012Phys. Rev. B252260View full textAdd to dashboardCite

“…We see that the phase stiffness relative to T c is weaker than in other Fe-based superconductors as well as the cuprates, even weaker than that in highly underdoped YBCO. 27,30,31 This may reflect a "Swiss cheese" like response of the system to impurities, indicating nanoscale inhomogeneity is likely present in 10-3-8. 32,33 Our measurement of λ is not sensitive to heterogeneity on this scale.…”