Electron- and hole-doping on ScH₂and YH₂: effects on superconductivity without applied pressure

We present the evolution of the structural, electronic, and lattice dynamical properties, as well as the electron-phonon (el-ph) coupling and superconducting critical temperature (T_c) of ScH₂and YH₂metal hydrides solid solutions, as a function of the electron- and hole-doping content. The study was performed within the density functional perturbation theory, taking into account the effect of zero-point energy through the quasi-harmonic approximation, and the solid solutions Sc_1-MH₂(M = Ca, Ti) and Y_1-MH₂(M = Sr, Zr) were modeled by the virtual crystal approximation. We have found that, under hole-doping (M = Ca, Sr), the ScH₂and YH₂hydrides do not improve their el-ph coupling properties, sensed byλ(x). Instead, by electron-doping (M = Ti, Zr), the systems reach a critical contentx≈ 0.5 where the latent coupling is triggered, increasingλas high as 70%, in comparison with itsλ(x= 0) value. Our results show thatT_cquickly decreases as a function ofxon the hole-doping region, fromx= 0.2 tox= 0.9, collapsing at the end. Alternatively, for electron-doping,T_cfirst decreases steadily untilx= 0.5, reaching its minimum, but forx> 0.5 it increases rapidly, reaching its maximum value of the entire range at the Sc_0.05Ti_0.95H₂and Y_0.2Zr_0.8H₂solid solutions, demonstrating that electron-doping can improve the superconducting properties of pristine metal hydrides, in the absence of applied pressure.