Observation of an oxygen isotope shift in the superconducting transition temperature of ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_4$

An oxygen isotope shift is observed in superconducting ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_4$ when ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ is substituted partially for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$; the superconducting transition temperature $T_c$ is lowered by 0.3 to 1.0 K in different samples. We examine these results using conventioanl phonon-mediated BCS theory and conclude that, for ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_4$, phonons play an important role in the pairing mechanism.