Superfluid response in monolayer high-T_c cuprates

We have studied the doping dependence of the in-plane and out-of-plane superfluid density ρ^s(0) of two-monolayer high-T_c superconductors, HgBa₂CuO_4+δ and La_2−xSr_xCuO₄, using the low-frequency ac susceptibility and the muon-spin-relaxation techniques. For both superconductors, ρ^s(0) increases rapidly with doping in the underdoped and optimally doped regimes and becomes nearly doping independent above a critical doping, p_c 0.20.