The oxygen-isotope (^16O/^18O) effect (OIE) on the in-plane penetration depth $\lambda_{ ab} (0)$ in underdoped Y_{ 1-x}Pr_xBa_2Cu_3O_{ 7-delta} was studied by muon-spin rotation. A pronounced OIE on $\lambda_{ ab}^{ -2}(0)$ was observed with a relative isotope shift of $\Delta\lambda^{ -2}_{ ab}/\lambda^{ -2}_{ ab}$=-5(2)% for x =0.3 and -9(2)% for x=0.4. It arises mainly from the oxygen-mass dependence of the in-plane effective mass $m_{ ab}^{ \ast}$. The OIE exponents of T_{ c} and of $\lambda_{ ab}^{ -2}(0)$ exhibit a relation that appears to be generic for cuprate superconductors.
Categories: cond-mat.supr-con