Fulltext summary
Summary
The paper explores superconductivity and ferroelectric orbital magnetism in semimetallic rhombohedral hexalayer graphene, identifying two superconducting states, SC1 and SC2, linked to Lifshitz transitions and band inversion as the electric field is tuned (Deng2026 pages 2-3). It reports temperature-dependent correlated and band insulating states, with a transport gap extracted using the formula Rxx ∝ e-Δ/2kBT (Deng2026 pages 12-16). The study reveals a multiferroic transition temperature above 3.6 K and examines Fermi surface evolution with doping, identifying transitions from a four-fold degenerate full metal to a half-metal state (Deng2026 pages 16-20). An orbital magnetic state with electric- and magnetic-field hysteresis is found, with polarity reversal across a critical electric field (Deng2026 pages 2-3). The research identifies phase boundaries and band inversions, revealing complex interactions between electric field, doping, and band structure (Deng2026 pages 4-6).
Methods
The study employs temperature-dependent transport measurements to extract the transport gap using the formula Rxx ∝ e-Δ/2kBT (Deng2026 pages 12-16). Quantum oscillations and FFT analyses are used to reveal complex Fermi surface features and Lifshitz transitions (Deng2026 pages 16-20). The impact of in-plane magnetic fields on superconducting states and phase boundaries is explored, noting the disappearance of the electron-hole Fermi liquid (Deng2026 pages 24-31). Electric-field-dependent magnetic hysteresis is analyzed to demonstrate electric and magnetic field control of ferrovalley orbital ferromagnetic states (Deng2026 pages 12-16). The study maps out a phase diagram with states like half metals and superconductivity, using doping and electric field variations to probe band structure changes (Deng2026 pages 4-6).
Rhombohedral multilayer graphene has emerged as a promising platform for exploring correlated and topological quantum phases, enabled by its Berry-curvature-bearing flat bands. While prior work has focused on separated conduction and valence bands, we probe the extensive semimetallic regime of rhombohedral hexalayer graphene. We survey a rich phase diagram dominated by flavor-symmetry breaking and reveal an electric-field-driven band inversion by fermiology. Near this inversion, we observe two superconducting-like states confined to regions with coexisting electron and hole Fermi surfaces, suggesting a possible dual-carrier origin. In addition, we identify a ferroelectric orbital magnet that undergoes sharp switching under unipolar electric fields, signaling spontaneous electric polarization. Unlike previously reported multiferroicity near zero electric field, this new state exhibits magnetic hysteresis reversible by electric field, consistent with a phenomenological model of coupled electric and magnetic polarization. Our work elucidates the correlated semimetal regime in rhombohedral graphene and underscores its potential to host diverse quantum phases.