Spontaneous spin superconductor state in ABCA-stacked tetralayer graphene

Abstract

We theoretically demonstrate a spontaneous spin superconductor (SC) state in ABCA-stacked tetralayer graphene, under sequential effects of electron-electron (e-e) and electron-hole (e-h) interactions. First of all, we examine the ferromagnetic (FM) exchange instability and phase diagram of the system induced by the e-e Coulomb interaction. At non- or low-doping levels, the interaction trends to stabilize an FM phase with the coexisting electron and hole carriers. Superior to bilayer and trilayer systems, tetralayer graphene has a larger FM phase region and spin splitting, making it more advantageous to realize the spin SC state. Subsequently, we prove that the FM state becomes unstable when attractive e-h interaction is considered at low temperature. As a consequence, the spin SC state can be spontaneously formed, where spin-triplet exciton pairs act as the equivalent of Cooper pairs. We further develop a consistent BCS-type theory for the spin SC state in ABCA-stacked graphene. The predicted spin superconducting gap can reach about 7.0meV, with a critical temperature of about 45 K for a nondoping system. At last, we demonstrated a spin-current Josephson effect in the ABCA-stacked graphene spin SC heterojunction. Our findings enrich the prospective spin SC candidate materials, illuminating more possibilities for achieving nondissipative superspintronics.

Similar papers