Electron- and hole-doping on ScH2 and YH2: effects on superconductivity without applied pressure

Abstract

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 ScH2 and YH2 metal 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−x M x H2 (M = Ca, Ti) and Y1−x M x H2 (M = Sr, Zr) were modeled by the virtual crystal approximation. We have found that, under hole-doping (M = Ca, Sr), the ScH2 and YH2 hydrides do not improve their el–ph 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 T c quickly 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, T c first 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 Sc0.05Ti0.95H2 and Y0.2Zr0.8H2 solid solutions, demonstrating that electron-doping can improve the superconducting properties of pristine metal hydrides, in the absence of applied pressure.