Chiral and topological superconductivity in isospin polarized multilayer graphene

A microscopic mechanism for chiral p-wave superconductivity from Coulomb repulsion is proposed for spin- and valley-polarized state of rhombohedral multilayer graphene. The superconducting instability arises when strong Thomas-Fermi screening of the Coulomb potential allows Friedel oscillations to take over – leading to an effective attraction on length scales below the Fermi wavelength. The superconducting critical temperature is largest at low density below a Lifshitz transition to an annular Fermi sea, where the additional pocket strongly enhances Thomas-Fermi screening. The Lifshitz transition also marks a topological phase transition from a trivial to a topological superconducting phase hosting Majorana fermions. The chirality of the superconducting order parameter is selected by the chirality of the valley-polarized Bloch electrons. Our results are in reasonable agreement with observations in a recent experiment on tetralayer graphene. Recently, chiral superconductivity has been observed in rhombohedral tetralayer graphene under electron doping, arising from a spin- and valley-polarized normal state. Here, the authors propose a superconducting mechanism based on over-screening of Coulomb interaction due to charge fluctuations.