The oxygen-isotope (^{ 16}O/^{ 18}O) effect (OIE) on the in-plane magnetic penetration depth \lambda_{ ab}(0) in optimally-doped YBa_2Cu_3O_{ 7-\delta} and La_{ 1.85}Sr_{ 0.15}CuO_4, and in slightly underdoped YBa_2Cu_4O_8 and Y_{ 0.8}Pr_{ 0.2}Ba_2Cu_3O_{ 7-\delta} was studied by means of muon-spin rotation. A substantial OIE on \lambda_{ ab}(0) with an OIE exponent \beta_O=-d\ln\lambda_{ ab}(0)/d\ln M_O\approx - 0.2 (M_O is the mass of the oxygen isotope), and a small OIE on the transition temperature T_c with an OIE exponent \alpha_O=-d\ln T_{ c}/d \ln M_O\simeq0.02 to 0.1 were observed. The observation of a substantial isotope effect on \lambda_{ ab}(0), even in cuprates where the OIE on T_c is small, indicates that lattice effects play an important role in cuprate HTS.
Categories: cond-mat.supr-con