Quantum structural fluxion in superconducting lanthanum polyhydride.
basic_science · Level V
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- Record sourced from PubMed, PMID 36966129.
- Also identified by DOI 10.1038/s41467-023-37295-1 and PMC identifier 10039887.
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Abstract
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<sub>9.6</sub> or LaH<sub>10±δ</sub> polyhydride responsible for the superconductivity, which in the literature is commonly treated as LaH<sub>10</sub> 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<sup>-7</sup> cm<sup>2</sup>/s in LaH<sub>9.63</sub> 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<sub>c</sub> 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.