Correlation between oxygen isotope effects on the transition temperature and the magnetic penetration depth in high-temperature superconductors close to optimal doping

TL;DR

This study investigates how oxygen isotope substitution affects the magnetic penetration depth and transition temperature in high-temperature superconductors, revealing significant lattice effects even when T_c changes minimally.

Contribution

It provides new experimental evidence linking oxygen isotope effects on magnetic penetration depth to lattice effects in cuprate superconductors.

Findings

Substantial isotope effect on magnetic penetration depth with eta_O  -0.2.

Small isotope effect on transition temperature with lpha_O  0.02 to 0.1.

Lattice effects are significant in high-temperature superconductivity.

Abstract

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.