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

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.