Superconducting Density of States from the Magnetic Penetration Depth of Electron-Doped Cuprates La₂₋ₓCeₓCuO₄₋y and Pr₂₋ₓCeₓCuO₄₋y

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From measurements of the magnetic penetration depth, λ(T), from 1.6 K to Tc in films of electron-doped cuprates La₂₋ₓCeₓCuO₄₋y and Pr₂₋ₓCeₓCuO₄₋y we obtain the normalized density of states, Nₛ(E) at T=0 by using a simple model. In this framework, the flat behavior of λ⁻²(T) at low T implies Nₛ(E) is small, possibly gapped, at low energies. The upward curvature in λ⁻²(T) near Tc seen in overdoped films implies that superfluid comes from an anomalously small energy band within about 3kBTc of the Fermi surface.