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 (Tc) 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 Tc 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.