Oxygen Isotope Effect in the High Temperature Superconductors YBa₂Cu₃O_7−δ and La_1.85Sr_0.15CuO₄, with ¹⁸O Substituted by Diffusion

Abstract

One of the most suggestive tests for electron-phonon coupling in conventional superconductors is the isotope effect, where T_c is sensitive to ionic mass: T_c ∝ M^−α. The presence of an isotope shift would demonstrate an important role played by the phonons in the superconductivity mechanism. The high-T_c superconducting oxide La_1.85Sr_0.15CuO₄ and YBa₂Cu₃O_7−δ have many structural¹ and electronic² features in common. An important feature common to both the layered perovskite K₂NiF₄ structure of La_2−xM_xCuO₄ (M = Ba, Sr, or Ca) and the distorted oxygen-defect pervoskite structure of RBa₂Cu₃O_7−δ (R = Y or some lanthanide rare-earth elements) is the existence of two-dimensional copper-oxygen planes which are most responsible for the metallic conduction.