Chiral d-wave superconducting state in the core of a doubly quantized s-wave vortex in graphene

We show that the intrinsic chiral (d(x2-y2) +/- id(xy))-wave superconducting pairing in doped graphene is significantly strengthened in the core region of a doubly quantized s-wave superconducting vortex produced in a graphene-superconductor hybrid structure. The chiral d-wave state is induced by the proximity effect, which transfers the center-of-mass angular momentum of the s-wave vortex to the orbital angular momentum of the chiral d-wave Cooper pairs. The proximity effect is enhanced by the circular geometry of the vortex and we find a [1 + (T -T-c,T-J)(2)](-1) temperature dependence for the chiral d-wave core amplitude, where T-c,T-J is its intrinsic bulk transition temperature. We further propose to detect the chiral d-wave state by studying the temperature dependence of the low-energy local density of states in the vortex core, which displays a sudden radial change as a function of the strength of the d-wave core state.