Discovery of High-Temperature Superconductivity (T<sub>c</sub> = 55 K) in B-Doped Q-Carbon.

Bhaumik, Anagh; Sachan, Ritesh; Gupta, Siddharth; Narayan, Jagdish · ACS Nano · 2017

basic_science · Level V

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Abstract

We have achieved a superconducting transition temperature (T<sub>c</sub>) of 55 K in 27 at% B-doped Q-carbon. This value represents a significant improvement over previously reported T<sub>c</sub> of 36 K in B-doped Q-carbon and is the highest T<sub>c</sub> for conventional BCS (Bardeen-Cooper-Schrieffer) superconductivity in bulk carbon-based materials. The B-doped Q-carbon exhibits type-II superconducting characteristics with H<sub>c2</sub>(0) ∼ 10.4 T, consistent with the BCS formalism. The B-doped Q-carbon is formed by nanosecond laser melting of B/C multilayered films in a super undercooled state and subsequent quenching. It is determined that ∼67% of the total boron exists with carbon in a sp<sup>3</sup> hybridized state, which is responsible for the substantially enhanced T<sub>c</sub>. Through the study of the vibrational modes, we deduce that higher density of states near the Fermi level and moderate to strong electron-phonon coupling lead to a high T<sub>c</sub> of 55 K. With these results, we establish that heavy B doping in Q-carbon is the pathway for achieving high-temperature superconductivity.