Strain-induced structural phase transition and superconductivity of the LiB₈ monolayer

The development of two-dimensional (2D) superconductors is imperative for advancing micro non-dissipative electronic devices and integrated circuits. Here, we identify a novel 2D superconductor, LiB₈ monolayer, with potential for fabrication through metal atom deposition onto χ₃ borophene sheets, by the CALYPSO structural searches method and first-principles calculations. The calculated results demonstrate that the stable LiB₈ monolayer exhibits Cmmm symmetry, displaying metallic behavior and intrinsic superconductivity. The superconducting transition temperature (T_c) of the LiB₈ monolayer is 22.2 K, motivated by the electron-phonon coupling (EPC) interactions originating from electrons of B atoms and phonons generated by atomic vibrations of Li and B atoms. More importantly, the LiB₈ monolayer undergoes a structural phase transition from Cmmm to Pmmm under uniaxial tensile strain. The Pmmm phase of the LiB₈ monolayer also exhibits notable superconductivity with a T_c value of 21.0 K. These findings enrich the 2D boron-based high-temperature superconductors and offer insights for the design of nanosized boron-based electronic devices.