Probing the order parameter and the c-axis coupling of high-T-c cuprates by penetration depth measurements

We have measured the low-temperature (T) dependence of the anisotropic penetration depth lambda(T) of magnetically aligned powders of HgBa2Can-1CunO2n+2+delta (n = 1 and 3) down to 1.2 K. For both members the T dependence of the in-plane penetration depth lambda(ab)(T) is strongly linear, whereas the out-of-plane component lambda(c)(T), for n = 1 and 3, varies as T-5 and T-2, respectively. For comparison, we also report A,(T) data for grain-aligned YBa2Cu3O7-delta (delta = 0.0 and 0.43) which vary as T and T-2, respectively. The results are discussed in terms of d(x2-y2)-wave symmetry Of the order parameter in cuprates.