One-Dimensional Hydrogen Chains in Li-Hf-H System: A Pathway to High Superconductivity Under High Pressure

The recent discovery of high-critical-temperature (high-T_c) superconductivity in hydrides such as H₃S and LaH₁₀ has significantly advanced the quest for room-temperature superconductors. This work reports a new class of high-T_c hydrides in the Li-Hf-H system characterized by unknown one-dimensional (1D) hydrogen chains. Through structure prediction methods and first-principles calculations, the thermodynamically stable compound LiHfH₂₀ is discovered, exhibiting a remarkable T_c of 222 K at 260 GPa. Notably, the distinct 1D hydrogen chains in LiHfH₂₀ facilitate strong coupling between high-frequency phonon modes and hydrogen-derived electronic states near the Fermi level, significantly enhancing superconductivity. Extending this concept to other MXH₂₀ compounds (M and X represent the other 27 elements), it is demonstrated that hole doping further increases the T_c, exemplified by isostructural BeCaH₂₀, which achieves a T_c of 262 K. These findings provide novel and viable high-pressure hydrides with 1D hydrogen chain for future experimental synthesis toward room-temperature superconductivity.