Strain Effect on the Superconductivity in Borophenes

The effects of strain on the structure stability, electron-phonon coupling (EPC), and superconductivity of two types of monolayer borophenes realized in the experiments are systematically investigated within the framework of density functional theory. We find that the electron-phonon coupling (EPC) in the buckled triangle borophene can be significantly enhanced by the suitable strain (-2-3%) due to the lower acoustic phonon branch softening. Our calculations suggest that a superconducting transition temperature (T-c) ranging from 24 to 32 K may be observed in the experiment. For the beta(12) borophene, the EPC constant (lambda) and T-c exhibit a U-curve variation with the strain ranging from 0 to 12%. The highest T-c of 14.9 K can be obtained in the pristine structure. The stiffness of the lower acoustic phonon branches and the U-curve variation of N(E-F) mainly from the p(z) electrons of boron are responsible for the change of the superconducting transition temperature with the increase of the tensile strain. Although borophenes have a highly anisotropic structure, the uniaxial strain effect on the superconductivity is isotropic.