Nonreciprocal Current-Induced Zero-Resistance State in Valley-Polarized Superconductors

The recently observed nonreciprocal current-induced zero-resistance state (CIZRS) in twisted trilayer graphene/WSe_{2} heterostructure has posed a significant theoretical challenge. In the experiment, the system shows a zero-resistance state only when a sufficiently large current is applied in a particular direction, while stays in an incipient superconducting state with small resistance when the current is small or flows in the opposite direction. In this Letter, we provide a theory of CIZRS. We show that the threefold degenerate Fulde-Ferrell (FF) states are stabilized by the valley polarization and trigonal warping effects of trilayer graphene/WSe_{2} heterostructures. Moreover, a current flowing in a particular direction breaks the threefold degeneracy and favors a particular FF pairing domain. We therefore propose that the incipient superconducting state is naturally understood as a multidomain state where the interdomain supercurrent is difficult to flow due to the tiny Josephson coupling caused by the mismatch of Cooper-pair momenta between different FF domains. Nevertheless, a sufficiently large current in a particular direction can selectively populate a certain FF state and create monodomain pathways with zero resistance. Crucially, due to the threefold symmetry of the system, a current flowing in the opposite direction can fail to generate the zero-resistance pathways, thus giving rise to the observed nonreciprocity. Finally, we suggest that the long-sought-after triangular finite-momentum state can also be realized in valley-polarized superconductors.