Low temperature magnetic penetration depth in d-wave superconductors

We briefly review the experimental results of the low temperature magnetic penetration depth λ(T) of d-wave superconductors. In very clean high-T_c superconductors (HTSC) the low temperature in-plane penetration depth λ_‖(T) varies linearly with T. A weaker power law temperature dependence is found for the out-of-plane penetration depth λ_⊥(T) in most of HTSC. In the organic superconductors κ-(BEDT-TTF)₂X X=Cu(NCS)₂, CuN(CN)₂]Br] and slightly dirty HTSC λ_‖∝bT²/(T*+T), where is deduced from an impurity scattering model. In clean CeCoIn₅ a crossover from linear to quadratic temperature behavior at low T was interpreted as the first evidence for nonlocal effects in a d-wave superconductor.