Anomalous metal and superconducting phases in rhombohedral graphene.

Two-dimensional superconductivity is now well established in graphene-based systems, with many such realizations showing evidence for unconventional pairing1-6. Yet, in several of the gate-tuned phases that otherwise exhibit clear signatures of superconductivity, the resistance does not vanish as temperature is lowered, instead saturating at a finite value2,6-15. Here we report a systematic study of this behaviour in rhombohedral graphene on a WSe2 substrate, finding regions of gate space with zero-resistance superconductivity alongside others with finite saturation resistance. At zero magnetic field, these regions appear as isolated pockets in gate space that otherwise exhibit very similar phenomenology, including abrupt transitions to the normal state as temperature, perpendicular magnetic field and current are raised above critical values. A small in-plane field expands and merges these pockets without qualitatively altering their behaviour, producing a sharp boundary at millikelvin base temperature between states of zero or finite resistance. The finite-resistance state reproduces key phenomenology associated with the anomalous metal, a state that has been observed in thin-film superconductors for decades but lacks an accepted theoretical explanation16,17. The tunability and reproducibility of ultra-clean rhombohedral graphene place strong constraints on extrinsic explanations and provide a new platform for understanding this behaviour.