Enhanced Superconductivity in X₄H₁₅ Compounds via Hole-Doping at Ambient Pressure

This study presents a computational investigation of X₄H₁₅ compounds (where X represents a metal) as potential superconductors at ambient conditions or under pressure. Through systematic density functional theory calculations and electron-phonon coupling analysis, it is demonstrated that electronic structure engineering via hole doping dramatically enhances the superconducting properties of these materials. While electron-doped compounds with X^{4 +} cations (Ti, Zr, Hf, Th) exhibit modest transition temperatures of 1-9 K, hole-doped systems with X^{3 +} cations (Y, Tb, Dy, Ho, Er, Tm, Lu) show remarkably higher values of ≈50 K at ambient pressure. Superconductivity in hole-doped compounds originates from stronger coupling between electrons and both cation and hydrogen phonon modes. Although pristine X^{3 +} ₄H₁₅ compounds are thermodynamically unstable, a viable synthesis route via controlled hole doping of the charge-compensated YZr₃H₁₅ compound is proposed. The calculations predict that even minimal concentrations of excess Y can induce high-temperature superconductivity while preserving structural integrity. This work reveals how strategic electronic structure modulation can optimize superconducting properties in hydride systems, establishing a promising pathway toward practical high-temperature conventional superconductors at ambient pressure.