Topological properties of Mo2C and W2C superconductors

The topological electronic properties of orthorhombic-phase ${\mathrm{Mo}}₂\mathrm{C}$ and ${\mathrm{W}}₂\mathrm{C}$ superconductors have been studied based on first-principles electronic structure calculations. Our studies show that both ${\mathrm{Mo}}₂\mathrm{C}$ and ${\mathrm{W}}₂\mathrm{C}$ are three-dimensional strong topological insulators defined on curved Fermi levels. The topological surface states on the (001) surface of ${\mathrm{Mo}}₂\mathrm{C}$ right cross the Fermi level, while those of ${\mathrm{W}}₂\mathrm{C}$ pass through the Fermi level with slight electron doping. These surface states hold helical spin textures and can be induced to become superconducting via a proximity effect, giving rise to an equivalent $p+ip$ type superconductivity. Our results show that ${\mathrm{Mo}}₂\mathrm{C}$ and ${\mathrm{W}}₂\mathrm{C}$ can provide a promising platform for exploring topological superconductivity and Majorana zero modes.