Coexistence of Superconductivity and Chern insulators with |C| $\geq 1$ in twisted rhombohedral bilayer-trilayer graphene

Abstract

Rhombohedral multilayer graphene (RMG) has been demonstrated as a promising platform for investigating strongly correlated phases of matter. Here, we observe a coexistence of superconductivity and Chern insulators in a twisted rhombohedral bilayer-trilayer graphene moiré superlattice. Superconductivity, evidenced by a sharp transition with a critical temperature of ~180 mK, nonlinear I-V with a BKT temperature of 135 mK, and a signature of phase-sensitive interference patterns, emerges from a symmetry-breaking Fermi surface near v = -2 and D = 0, and it survives at a large in-plane magnetic field up to 2 T, strongly deviating from the Pauli limit. Moreover, we observe a strong modulation of the Ginzburg-Landau coherence length from 467 nm to 145 nm as the in-plane magnetic field increases from 0 to 2 T, whereas the critical current Ic barely changes. Unlike previous studies in RMG, we observe a competition between superconductivity and a correlated insulator at v = -2, monitored by displacement fields and twist angles. Note that we also observe integer Chern insulators with C = 1, 3, and -3 at v = 1/2, 1, and 3, respectively, for large D > 0 in the same superconducting device. The observations establish twisted rhombohedral graphene multilayers as a fascinating system to investigate unconventional superconductivity, high Chern number topology, and their interplay.