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Title: Is rhombohedral graphene a chiral topological superconductor
Plain: Tetralayer and pentalayer graphene superconduct out of a state in which electron spins and valleys (the two inequivalent momentum regions where graphene's low-energy electrons are found) are aligned, and the superconductor shows magnetic hysteresis, suggesting pairs that rotate in one direction (chiral pairing).
Precise: Han et al. (Nature 643, 654, 2025) found two superconducting states with $T_c$ up to 300 mK at $n$ down to $2.4e11\,\mathrm{cm}^{-2}$ in rhombohedral tetralayer and pentalayer graphene without moire, emerging from a spin- and valley-polarized quarter metal and showing anomalous-Hall hysteresis. Determine the pairing symmetry and whether the state is topological, i.e., its Bogoliubov Chern number and number of chiral Majorana edge modes. An answer gives both with direct evidence.
Settled by: Thermal Hall conductance $\kappa_{xy}/T$ at $T << T_{\mathrm{c}}$ or edge tunnelling revealing chiral Majorana modes, plus phase-sensitive Josephson tests.
Kind: well-posed
Answer type: classification
References: (empty)
Literature status: open
Status note: 2025 transport gives evidence of time-reversal breaking; no edge-mode or phase-sensitive measurement as of 2026.
Posed since: 2025