Oxygen-isotope effect on the in-plane penetration depth in underdoped Y₁₋ₓPrₓBa₂Cu₃O7-delta as revealed by muon-spin rotation

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The oxygen-isotope (¹6O/¹8O) effect (OIE) on the in-plane penetration depth λab (0) in underdoped Y₁₋ₓPrₓBa₂Cu₃O7-delta was studied by muon-spin rotation. A pronounced OIE on λab⁻²(0) was observed with a relative isotope shift of Δλ⁻²ab/λ⁻²ab=-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 mab. The OIE exponents of Tc and of λab⁻²(0) exhibit a relation that appears to be generic for cuprate superconductors.