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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 coupling and superconducting critical temperature (Tc) 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 Sc1-xMxH2(M=Ca,Ti) and Y1-xMxH2(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 electron-phonon coupling properties, sensed by λ(x). Instead, by electron-doping (M=Ti,Zr), the systems reach a critical content x≈0.5 where the latent coupling is triggered, increasing λ as high as 70%, in comparison with its λ(x = 0) value. Our results show that Tcquickly decreases as a function of x on the hole-doping region, from x = 0.2 to x = 0.9, collapsing at the end. Alternatively, for electron-doping, Tcﬁrst decreases steadily until x = 0.5, reaching its minimum, but for x > 0.5 it increases rapidly, reaching its maximum value of the entire range at the Sc0.05Ti0.95H2and Y0.2Zr0.8H2solid solutions, demonstrating that electron-doping can improve the superconducting properties of pristine metal hydrides, in the absence of applied pressure.