Key Laboratory for Photonic and Electronic Bandgap Materials (Ministry of Education), School of Physics and Electronic Engineering, Harbin Normal University, 150025, Harbin, China.
International Center for Computational Method & Software, College of Physics, Jilin University, 130012, Changchun, China.
Nat Commun. 2023 Mar 25;14(1):1674. doi: 10.1038/s41467-023-37295-1.
The discovery of 250-kelvin superconducting lanthanum polyhydride under high pressure marked a significant advance toward the realization of a room-temperature superconductor. X-ray diffraction (XRD) studies reveal a nonstoichiometric LaH or LaH polyhydride responsible for the superconductivity, which in the literature is commonly treated as LaH without accounting for stoichiometric defects. Here, we discover significant nuclear quantum effects (NQE) in this polyhydride, and demonstrate that a minor amount of stoichiometric defects will cause quantum proton diffusion in the otherwise rigid lanthanum lattice in the ground state. The diffusion coefficient reaches ~10 cm/s in LaH at 150 gigapascals and 240 kelvin, approaching the upper bound value of interstitial hydrides at comparable temperatures. A puzzling phenomenon observed in previous experiments, the positive pressure dependence of the superconducting critical temperature T below 150 gigapascals, is explained by a modulation of the electronic structure due to a premature distortion of the hydrogen lattice in this quantum fluxional structure upon decompression, and resulting changes of the electron-phonon coupling. This finding suggests the coexistence of the quantum proton fluxion and hydrogen-induced superconductivity in this lanthanum polyhydride, and leads to an understanding of the structural nature and superconductivity of nonstoichiomectric hydrogen-rich materials.
高压下 250 开尔文超导镧多氢化物的发现标志着室温超导体实现的重大进展。X 射线衍射 (XRD) 研究表明，非化学计量的 LaH 或 LaH 多氢化物是超导的原因，在文献中通常将其视为 LaH，而不考虑化学计量缺陷。在这里，我们在这种多氢化物中发现了显著的核量子效应 (NQE)，并证明在基态下，少量的化学计量缺陷会导致原本刚性的镧晶格中的量子质子扩散。在 150 吉帕斯卡和 240 开尔文下，LaH 中的扩散系数达到~10cm/s，接近可比温度下间隙氢化物的上限值。在以前的实验中观察到的一个令人困惑的现象是，超导临界温度 T 在 150 吉帕斯卡以下的正压依赖性，这是由于在这种量子流变体结构中，氢晶格在减压时过早变形，导致电子结构的调制，以及电子-声子耦合的变化所解释的。这一发现表明，在这种镧多氢化物中存在量子质子流和氢诱导超导的共存，并导致对非化学计量富氢材料的结构性质和超导性的理解。
