Archive

Opening questions

On the Scout's desk

1. Prediction of High Tc Superconductivity in Hole-doped LiBC

   arXiv:cond-mat/0111592 · 2001 · H. Rosner, A. Kitaigorodsky, W. E. Pickett

   The layered lithium borocarbide LiBC, isovalent with and structurally similar to the superconductor MgB2, is an insulator due to the modulation within the hexagonal layers (BC vs. B2). We show that hole-doping of LiBC results in Fermi surfaces of B-C p sigma character that couple very strongly to B-C bond stretching modes, precisely the features that lead to superconductivity at Tc = 40 K in MgB2. Comparison of Li{0.5}BC with MgB2 indicates the former to be a prime candidate for electron-phonon coupled superconductivity at substantially higher temperature than in MgB2.

2. Searching Materials Space for Hydride Superconductors at Ambient Pressure

   arXiv:2403.13496 · 2024 · Tiago F. T. Cerqueira, Yue-Wen Fang, Ion Errea et al.

   We employed a machine-learning assisted approach to search for superconducting hydrides under ambient pressure within an extensive dataset comprising over 150 000 compounds. Our investigation yielded around 50 systems with transition temperatures surpassing 20 K, and some even reaching above 70 K. These compounds have very different crystal structures, with different dimensionality, chemical composition, stoichiometry, and arrangement of the hydrogens. Interestingly, most of these systems displayed slight thermodynamic instability, implying that their synthesis would require conditions beyond ambient equilibrium. Moreover, we found a consistent chemical composition in the majority of these s

3. Superconducting boron doped nanocrystalline diamond on boron nitride ceramics

   arXiv:1905.02979 · 2019 · Soumen Mandal, Henry A. Bland, Jerome A. Cuenca et al.

   In this work we have demonstrated the growth of nanocrystalline diamond on boron nitride ceramic. We measured the zeta potential of the ceramics to select the diamond seeds. Diamond was then grown on the seeded ceramics using a microwave chemical vapour deposition system. A clear difference was found between the samples which were seeded with nanodiamond and the ones not seeded before growth. Raman spectroscopy confirmed the excellent quality of the diamond film. Dielectric measurements showed an increase in the dielectric constant of the material after diamond growth. The diamond was also doped with boron to make it superconducting. The film had a transition temperature close to 3.4K. Simil

4. Na-catalyzed rapid synthesis and characterization of intercalated graphite CaC6

   arXiv:2309.01942 · 2023 · Akira Iyo, Hiroshi Fujihisa, Yoshito Gotoh et al.

   In this study, we conducted experiments on CaC6 for elucidating the Na-catalyzed formation mechanism and achieving rapid mass synthesis of graphite intercalation compounds (GICs). Rapidly synthesized CaC6 was characterized by analysis of its crystal structure and physical properties. We found that the formation of the reaction intermediate Na-GIC (NaCx, x = 64) requires a larger amount of Na than is intercalated between the graphite interlayers. The requirement for excess Na may provide insights into the mechanism of Na-catalyzed GIC formation. A Na-to-C molar mixing ratio of 1.5-2.0:6 was suitable for the efficient formation of CaC6 under heat treatment at 250°C for 2 h, and the catalytic N

5. High-Tc Superconductivity in doped boron-carbon clathrates

   arXiv:2110.05333 · 2021 · Simone Di Cataldo, Shadi Qulaghasi, Giovanni B. Bachelet et al.

   We report a high-throughput ab-initio study of the thermodynamic and superconducting proper- ties of the recently synthesized XB3C3 clathrates. These compounds, in which boron and carbon form a sponge-like network of interconnected cages each enclosing a central X atom, are attractive candidates to achieve high-Tc conventional superconductivity at ambient pressure, due to the simultaneous presence of a stiff B-C covalent network and a tunable charge reservoir, provided by the guest atom. Ternary compounds like CaB3C3, SrB3C3 and BaB3C3 are predicted to exhibit Tc 50 K at moderate or ambient pressures, which may further increase up to 77 K if the original comp

6. The Maximum Tc of Conventional Superconductors at Ambient Pressure

   arXiv:2502.18281 · 2025 · Kun Gao, Tiago F. T. Cerqueira, Antonio Sanna et al.

   The theoretical maximum critical temperature (Tc) for conventional superconductors at ambient pressure remains a fundamental question in condensed matter physics. Through analysis of electron-phonon calculations for over 20,000 metals, we critically examine this question. We find that while hydride metals can exhibit maximum phonon frequencies of more than 5000 K, the crucial logarithmic average frequency ωlog rarely exceeds 1800 K. Our data reveals an inherent trade-off between ωlog and the electron-phonon coupling constant λ, suggesting that the optimal Eliashberg function that maximizes Tc is unphysical. Based on our calculations, we identify Li2AgH6 and