The isotope effect in H3S superconductor

The experimental value of H3S a 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 in the harmonic approximation. 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.