Effects of anharmonic phonons on superconductivity in the NH4-intercalated boron-carbon clathrate NH4B2C8

Abstract

Achieving structural stability and high critical temperature (Tc) in hydrides under ambient conditions remains a major challenge. A feasible design strategy integrates the advantages of two material classes: (i) B-C–based clathrate superconductors, which exhibit excellent structural stability at ambient or relatively low pressures, and (ii) hydrogen-based unit, which possesses the potential for high Tc. Guided by this strategy, we theoretically predict a hypothetical compound NH4B2C8 by embedding hydrogenated units into a B-C clathrate framework. Using the stochastic self-consistent harmonic approximation combined with machine-learning-accelerated structural sampling, we assess the impact of anharmonicity on its superconducting properties. Anharmonic effects harden the dominant phonon modes 13–15, reducing the electron-phonon coupling constant λ from 1.43 to 1.22 and lowering Tc from 102 to 91 K. Furthermore, hole doping realized by NH4 vacancy engineering, which yields (NH4)3(B2C8)4, is demonstrated to be ineffective in enhancing Tc under anharmonic conditions. Our results highlight the synergistic role between hydrogen units and B-C frameworks in enhancing superconductivity, and underscore the importance of anharmonicity in the design of such superconductors.

Source-reported materials — not catalogue approval

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