Hydrogen Confined in a Single Wall Carbon Nanotube Becomes a Metallic and Superconductive Nanowire under High Pressure.

Metallic hydrogen is a long-desired material. However, the pressure needed to metallize hydrogen is difficult to access experimentally. We demonstrated that the high-density of hydrogen confined in a (8,0) single-wall carbon nanotube (SWNT) can be metallized at a relative low pressure of 163.5 GPa, due to the " physical compression" effect of SWNT. Through mimicking experimental measurements of the specific heat of confined hydrogen nanowire, we showed that the electronic specific heat of the hydrogen has a clear jump around 225 K, verifying a superconducting transition at this critical temperature. The superconducting hydrogen can be very well explained by the Eliashberg superconductivity theory for an electron-phonon strong-coupling system. Our simulation results open an avenue for the study of nanohydrogen materials at high pressure.