Theoretical prediction of superconductivity in two-dimensional hydrogenated metal diboride: M₂B₂H (M = Al, Mg, Mo, W)

In recent years, superconductivity in two-dimensional (2D) layered metal borides has aroused much interest. Here, based on first-principles calculations, we theoretically report four 2D hydrogenated metal diborides: M2B2H (M = Al, Mg, Mo, W), and investigate their geometrical structures, electronic structures, phonon and so on. Results reveal that the introduction of hydrogen atoms expands the frequency range of the phonon spectrum of monolayer M2B2, and significantly increases the EPC. We systematically analyze the specific origins of superconductivity in these hydrogenated low-dimensional systems. The obtained EPC constants lambda of M2B2H (M = Al, Mg, Mo, W) are 2.93, 0.86, 1.09, and 1.40, and the corresponding superconducting transition temperatures (T-c) are 52.6, 23.2, 21.5, and 18.6 K, respectively. By further applying electron/hole doping or biaxial tensile strain, the T-c can be further increased, with the highest T-c of 60.2 K in Al2B2H under 0.4% biaxial tensile strain. The predicted M2B2H provides a new platform for 2D superconductivity and may have potential applications in 2D nanodevices.