Nonlocal effects on the magnetic penetration depth in d-wave superconductors

8We show that, under certain conditions, the low temperature behavior of the magnetic penetration depth λ(T) of a pure d-wave superconductor is determined by nonlocal electrodynamics and, contrary to the general belief, the deviation Δλ(T) = λ(T) - λ(0) is proportional to T² and not T. We predict that the Δλ(T) ∝ T² dependence, due to nonlocality, should be observable experimentally in nominally clean high-T_c superconductors below a crossover temperature T* = (ξ₀/λ₀)Δ₀ ∼ 1 K. Possible complications due to impurities, surface quality, and crystal axes orientation are discussed.