Enhanced Superconducting Diode Effect due to Coexisting Phases

The superconducting diode effect refers to an asymmetry in the critical supercurrent Jc(n) along opposite directions, Jc(n) # Jc(-n). While the basic symmetry requirements for this effect are known, it is, for junction -free systems, difficult to capture within current theoretical models the large current asymmetries Jc(n)/Jc(-n) recently observed in experiment. We here propose and develop a theory for an enhancement mechanism of the diode effect arising from spontaneous symmetry breaking. We show-both within a phenomenological and a microscopic theory-that there is a coupling of the supercurrent and the underlying symmetry -breaking order parameter. This coupling can enhance the current asymmetry significantly. Our work might not only provide a possible explanation for recent experiments on trilayer graphene but also pave the way for future realizations of the superconducting diode effect with large current asymmetries.