Superconductor-Normal first order phase transition in the A15 phase of alkali-doped fullerides

Using a recently developed effective model[1], we study the superconductor-normal phase transition of alkali-doped fullrides. First, we use a simple mean field theory to decouple the inverted Hund’s coupling term and the on-site repulsive term in the Hamiltonian. Then, by analyzing the Helmholtz free energy, we show that the superconductor-normal phase transition is a first order one. Second, we use a slave-rotor approach and a Hartree-Fock mean-field theory to investigate the normal phase where we find a Mott-insulating, a Fermi liquid metal, and a spin-density wave phases as a result of the competition between interacting term and the kinetic energy term in the effective Hamiltonian. Finally, we construct the global phase diagram of the body-centered cubic structured alkali-doped fullerides in the temperature-pressure parameter space.

[1] Theja N. De Silva, Phys. Rev. B 100, 155106 (2019).