Evidence for Nodal Quasiparticles in Electron-Doped Cuprates from Penetration Depth Measurements

This is the authors' abstract. We don't add key points for this paper.

The in-plane magnetic penetration depth, λ(T), was measured down to 0.4 K in single crystals of electron-doped superconductors, Pr1.85Ce0.15CuO_4-δ (PCCO) and Nd1.85Ce0.15CuO_4-δ (NCCO). In PCCO, the superfluid density varies as T² from 0.025 up to roughly 0.3T/Tc suggestive of a d-wave state with impurities. In NCCO, λ(T) shows a pronounced upturn for T<4K due to the paramagnetic contribution of Nd³⁺ ions. Fits to an s-wave order parameter over the standard BCS range (T/Tc0ex0ex=0ex0ex0.32) limit any gap to less than Δₘᵢₙ(0)/Tc0ex0ex=0ex0ex0.57 in NCCO. For PCCO, the absence of paramagnetism permits a lower temperature fit and yields an upper limit of Δₘᵢₙ(0)/Tc0ex0ex=0ex0ex0.2.