Momentum-polarized superconductivity in twisted trilayer graphene

The spin-configuration of a Cooper pair is often informative of the pairing symmetry. According to the BCS theory, a conventional, s-wave superconductor arises from Cooper pairing in the singlet channel. Whereas a triplet Cooper pair is directly linked to a spatial wavefunction in the p- or f-wave channel, a hallmark of unconventional superconductivity. In multilayer graphene, the nature of the pairing instability is further complicated by emergent orders in the momentum-space, such as valley and momentum polarization. The presence of momentum-space instability suggests that the spin channel alone is insufficient to describe the superconducting pairing symmetry. In this work, we use angle-resolved nonreciprocal transport measurement to investigate the influence of momentum-space instabilities. We uncover a new cascade phenomenon across the moiré band fillings, where a series of transitions between momentum-polarized states appear outside the regular sequence of Dirac revivals. Moreover, we identify a new aspect of superconductivity, which is defined by its coexistence with spontaneous momentum polarization. Our findings point towards a direct link between spontaneously broken rotational and time-reversal symmetries, which has intriguing implications on the nature of the pairing instability.