Isotope Effect on the Electronic Spin Density in PdH Superconductor

Abstract

The nuclear spin-lattice relaxation rates of ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{D}$ in stoichiometric PdH and PdD indicate a significant increase in the spin density at the deuteron site over that at the proton site. The results are analyzed theoretically in two distinctly different models involving the zero-point vibrations of the hydrogen. The implication of these results for the understanding of the reverse isotope effect on $T_c$ is discussed.