Probing pairing symmetry of Sm1.85Ce0.15CuO4 via highly-sensitive voltage measurements: Evidence for strong impurity scattering

Using a highly-sensitive home-made mutual-inductance technique, temperature profiles of the magnetic penetration depth λ(T) in the optimally-doped Sm1.85Ce0.15CuO4 thin films have been extracted. The low-temperature behavior of λ(T) is found to be best-fitted by linear Δλ(T)/λ(0)=ln(2)kBT/Δ0 and quadratic Δλ(T)/λ(0)=Γ−1/2Δ0−3/2T2 laws above and below T=0.22TC, respectively, which clearly indicates the presence of d-wave pairing mechanism dominated by strong paramagnetic scattering at the lowest temperatures. The best fits produce Δ0/kBTC=2.07 and Γ/TC=0.25(TC/Δ0)3 for the estimates of the nodal gap parameter and impurity scattering rate.