Superconductivity of graphenelike hydrogen in H2He at high pressure

The structural diversity of hydrogen under high pressure is crucial for understanding its physical properties, especially for the superconductivity. Here, a combination of crystal structure prediction and first-principle calculations has predicted a metastable ${\mathrm{H}}_{2}\mathrm{He}$ at ultrahigh pressure of 800 GPa, where H atoms are arranged in graphenelike structure. ${\mathrm{H}}_{2}\mathrm{He}$ shows weak superconductivity with critical temperature of 4 K, which significantly increases to 155 and 201 K at electron doping of 0.6 and 1.2 $e$, respectively. Analysis suggests that the enhanced superconductivity is closely associated with the graphenelike H sublattice. The doped electrons almost transfer to H sublattice, inducing the increased H-derived density of states at the Fermi level, as well as their coupling with the phonon modes of graphenelike H layers. The current results could stimulate the experiment to search for more diverse hydrogen species at high pressure and provide a feasible way to design high-${T}_{\text{c}}$ superconductors as well.