Andreev conductance in the d+i d′ -wave superconducting states of graphene

We show that effective superconducting orders generally emerge at low energy in the superconducting state of graphene with conventionally defined pairing symmetry. We study a particular interesting example, the d x2 - y2 +i d xy ′ spin singlet pairing state in graphene which can be generated by electronic correlation. We find that effectively the d+i d′ -wave state is a state with mixed s -wave and exotic p+ip -wave pairing orders at low energy. This remarkable property leads to distinctive superconducting gap functions and behavior of the Andreev conductance spectra through a normal/superconducting graphene structure.