Research Progress on High-Temperature H2-Molecular-Type Hydride under High Pressure
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摘要: 室温超导体LaSc2H24的合成标志着人类在高压超导研究领域迈入一个崭新的阶段。未来富氢高温超导体研究的核心挑战之一在于降低晶体结构稳定存在的压力，从而为实现低压乃至常压室温超导提供坚实的理论基础与可行的技术路径。综述了近年来在氢化物超导体预测与实验合成方面的最新进展，重点探讨了一种实现低压高温超导的新策略—H2分子型氢化物，并重新审视了H2分子单元参与超导的起因，为理解声子介导的超导现象提供了新的视角。在H2分子型氢化物中，明显观察到近似自由电子气的行为，这些自由电子气表现出金属键特性，同时，分子氢结构未发生分解。这表明，超导转变的关键条件是存在形成库珀对的电子费米海，而非完全解离为原子态氢。H2分子型氢化物中自由电子气的形成机制可通过有限深势阱模型得到合理解释。此类材料在高压下的独特电子行为及其强电声耦合作用为设计低压、高温甚至室温超导材料开辟了全新的范式。Abstract: The synthesis of the room-temperature superconductor LaSc2H24 represents a significant milestone in the field of superconductivity research. A central goal of subsequent studies is to lower the stabilization pressure required for hydrogen-rich superconductors, thereby establishing both theoretical foundation and technical pathway toward achieving low-pressure room-temperature superconductivity. This paper reviews recent advances in the prediction and experimental synthesis of hydride materials, with a focus on a promising strategy for realizing high-temperature superconductivity at reduced pressures—namely, H2-molecular-typehydride. The superconducting mechanism dominated by molecular H2 units is redefined, offering a new perspective for understanding phonon-mediated superconductivity. In H2-molecular-type hydrides, a nearly free-electron gas behavior has been clearly observed. These delocalized electrons exhibit metallic bonding characteristics while retaining fragments of molecular hydrogen. This finding indicates that the essential condition for superconducting transition is the formation of a Fermi sea hosting Cooper pairs, rather than complete dissociation into atomic hydrogen. The generation mechanism of the free-electron gas in these materials can be effectively explained using a finite potential well model. The distinctive electronic properties of these compounds under high pressure, combined with enhanced electron-phonon coupling, establish a novel paradigm for designing low-pressure, high-temperature, and potentially room-temperature superconductors.
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图 4 H2分子型氢化物NaH10的(a)结构，(b)电子局域化函数的三维等值面，(c)声子色散曲线、声子态密度和Eliashberg谱函数α2F(ω)以及电声耦合常数的积分λ(ω)，(d)电子能带结构和投影态密度[16]
Figure 4. (a) Structure, (b) three-dimensional isosurface of the electron localization function (ELF), (c) phonon dispersion curves, phonon density of states (PHDOS), and Eliashberg spectral function α2F(ω) together with the integral λ(ω), (d) electronic band structure and projected density of states (PDOS) of H2-molecular-type hydrides NaH10[16]
图 5 H2分子型氢化物CaH14中(a) Kohn-Sham有效局域势的分布以及(b) −10.0 eV处的等势面，(c)选定Ca原子的3d（顶部）和2d（底部）势面的截面，(d)当2个有限势阱接近时脊处电位降低示意图（d0为2个势阱之间的给定初始距离）[19]
Figure 5. (a) Distribution of Kohn-Sham effective local potential; (b) the equipotential surface at −10.0 eV in H2-molecular-type hydrides CaH14; (c) the section of 3d (top) and 2d (bottom) potential surface for selected Ca atoms; (d) schematic illustration of potential decrease at the ridge as two finite potential wells approach, where d0 is a given initial distance between two potential well[19]
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