  A new two-dimensional material { Mg2B4C2, belonging to the family of the
conventional superconductor MgB2, is theoretically predicted to exhibit
superconductivity with critical temperature Tc estimated in the 47-48 K range
(predicted using the McMillian-Allen-Dynes formula) without any tuning of
external parameters such as doping, strain, or substrate-induced effects. The
origin of such a high intrinsic Tc is ascribed to the presence of strong
electron-phonon coupling and topological Dirac states (which are absent in
MgB2) yielding a large density of states at the Fermi level. This material also
features a nontrivial electronic band topology exhibiting Dirac points,
practically gapless Dirac nodal lines, and topological nontrivial edge states.
Consequently, it is a potential candidate for realization of topological
superconductivity in 2D. This system is obtained after replacing the chemically
active boron layers in MgB2 by chemically inactive boron-carbon layers. Hence,
the surfaces of this material are inert. Our calculations confirm the stability
of 2D Mg2B4C2. We also find that the key features of this material remain
essentially unchanged when its thickness is increased by modestly increasing
the number of inner MgB2 layers.
