Manipulating the electronic structure and superconductivity of Li₂B₃C by biaxial strain

Strain is a clean and efficient method to manipulate physical properties without changing the chemical composition. In this paper, we perform a systematic first-principles study of how biaxial strain manipulates the electronic structure and phonon-mediated superconductivity of Li₂B₃C with its optimal configuration. Here we introduce a descriptor Δε, defined as the energy offset between the B–B bridge σ-bonding band maximum and the Fermi level. We screen the biaxial-strained Li₂B₃C structures in the range of −5% to +5% and retain those with Δε > 0.05 eV for subsequent electron-phonon coupling (EPC) calculations. The maximum T_c = 44.72 K occurs at +5% a-axis strain and −5% b-axis strain. We then elucidate the microscopic mechanism underlying the strain response of the electronic structure by analyzing the corresponding changes of the structure and tight-binding parameters. Taking the optimal biaxial-strained Li₂B₃C as an example, we analyze its phonon properties and discuss the origin of its strong EPC. Our work provides reliable theoretical guidance for manipulating electronic structure and superconductivity by strain, and sheds new light on high-T_c superconductivity induced by metallic σ-bonding electrons.