Superconducting Density of States from the Magnetic Penetration Depth of Electron-Doped Cuprates La_(2-x)Ce_xCuO_(4-y) and Pr_(2-x)Ce_xCuO_(4-y)

From measurements of the magnetic penetration depth, $\lambda(T)$, from 1.6 K to $T_c$ in films of electron-doped cuprates La$_{2-x}$Ce$_x$CuO$_{4-y}$ and Pr$_{2-x}$Ce$_x$CuO$_{4-y}$ we obtain the normalized density of states, $N_s(E)$ at T=0 by using a simple model. In this framework, the flat behavior of $\lambda^{-2}(T)$ at low $T$ implies $N_s(E)$ is small, possibly gapped, at low energies. The upward curvature in $\lambda^{-2}(T)$ near $T_c$ seen in overdoped films implies that superfluid comes from an anomalously small energy band within about $3k_BT_c$ of the Fermi surface.