Effects of the Cu-O chains on the anisotropic penetration depth ofYBa2Cu4O8

Abstract
The temperature, T, dependence of the magnetic penetration depth, λ, of grain-aligned YBa2Cu4O8 has been measured along the ab plane and c axis. Both λab(T) and λc(T) vary as T up to 0.4Tc implying a square-root density of states at low energy. The results are discussed in terms of a proximity model of alternating stacked superconducting and normal layers.
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