Superconductivity of Cs$_3$C$_{60}$ at atmosphere pressure

Abstract

Pressure as a clean and efficient tool can bring about unexpected extraordinary physical and chemical properties of matters. The recent discoveries of superconductivity at nearly room temperature in hydrides highlight the power of pressure in this aspect. Capturing such Tc superconductivity at atmosphere pressure for the technological applications is highly desired. The large-scale growth of diamond through the chemical vapor deposition away from the usual high-pressure and high-temperature conditions fuels such a hope. Similar to hydrides, Cs-doped C$_{60}$ was also found to exhibit superconductivity by the application of pressure with a comparable Tc of 40 K as MgB$_2$. Here, we report the successful realization of superconductivity in Cs-doped C$_{60}$ at atmosphere pressure. The phase is characterized to have the primitive cubic structure in the space group of Pa-3 with the stoichiometry of Cs$_3$C$_{60}$. The superconductivity is evidenced from the observations of both the Meissner effect and zero-resistance state. Although the pressure effects on superconductivity are different for the newly discovered Cs$_{3}$C$_{60}$ compared to the known two phases with fcc and A15 structure, the evolution of Tc with the volume for all these superconductors follows the same universal trend, suggesting the same pairing mechanism of the superconductivity. Such a trend together with the nearly linear Tc vs the lattice constant in the structure with smaller unit-cell volumes and the neighbouring antiferromagnetic state in the structure with larger unit-cell volumes invites the electron-phonon coupling and the electron correlations together to account for the superconductivity in Cs$_3$C$_{60}$. The present results and findings suggest a new route to capturing the superconductivity which takes place at high pressures to atmosphere pressure environment.