Optimal coloring and strain-enhanced superconductivity in LinBn+1Cn−1

Boron-rich lithium borocarbides are promising candidates for phonon-mediated high-temperature superconductors due to their metallic σ-bonding electrons. Here, we use the cluster expansion method to identify energetically stable configurations (colorings) of Li2B3C and Li3B4C2, which are characterized by a distinctive pattern of alternating B-B and B-C zigzag chains. Surprisingly, the optimal configuration of Li2B3C exhibits an extremely low superconducting transition temperature of Tc < 0.03 K, which is attributed to the suppression of deformation potentials near the Fermi level caused by the specific electron filling of B-B zigzag chains. However, the σ-bonding electrons at the Fermi level are highly sensitive to external strain or pressure. Specifically, applying a −5% compressive uniaxial strain can significantly enhance the electron-phonon coupling and the Eliashberg spectral function, boosting up Tc to 37 K. This work not only presents a strategy for achieving high critical temperatures in LinBn+1Cn+1 compounds, but also provides valuable insights into the complex interplay between electronic structure and superconducting interaction. Boron-rich lithium borocarbides LinBn+1Cn-1 are MgB2-like candidates for phonon-mediated superconductivity, but the colouring of B/C atoms is unclear. Using first principles calculations, the authors find that Li2B3C with optimal colouring and Tc