The isotope effect in Hrm₃S superconductor

The experimental value of ${\rm H_{3}S}$ isotope coefficient decreases from $2.37$ to $0.31$ in the pressure range from $130$ GPa to $200$ GPa. We have shown that the value of $0.31$ is correctly reproduced in the framework of the classical Eliashberg approach. On the other hand, the anomalously large value of the isotope coefficient ($2.37$) may be associated with the strong renormalization of the normal state by the electron density of states.