Oxygen isotope effect on critical temperature and phonon modes in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$

The effect of oxygen isotope substitution on ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ has been studied. Powder samples in which ∼90% of the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ has been replaced by ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ have been prepared by gas exchange and compared to ${}_{}{}^{16}{}_{}{}^{}\mathrm{-}_{}^{16}{}_{}{}^{}$O exchanged samples. The phonon frequencies, measured by far infrared spectroscopy, are reduced after ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ exchange. Magnetic measurements of the superconducting transition temperature find a shift of 0.16±0.06 K, corresponding to α=0.017±0.006 in the Bardeen-Cooper-Schrieffer relation $T_c$∝$M^{\mathrm{-}\alpha }$. .AE