Observation of Integer and Fractional Chern insulators in high Chern number flatbands (2507.09908v1)

Abstract: The intertwined electron correlation and topology give birth to emergent quantum phenomena with fractionalized phases in condensed matter physics. Recently, Chern insulators and fractional ones with C smaller than one have been observed in twisted MoTe2 and rhombohedral pentalayer graphene-hBN moire systems at zero magnetic fields, resembling the fractional quantum Hall phases at high magnetic fields. Here, we target topological phases with high Chern number C > 1 by designing a new moire system, i.e. twisted rhombohedral trilayer-bilayer graphene. We observe Chern insulators with C = 3 at both v = 1 and v = 3. In particular, quantized anomalous Hall effect with C = -3 is observed at v = 3 for device D2. Most importantly, by fractionally filling the high Chern number flat band, we observe evidence of a fractional Chern insulator with C = -3/2 developing from even-denominator fractional filling v = 5/2 at zero magnetic fields, which reaches a fractionally quantized Hall effect with C = -3/2 (a quantization accuracy of 96%) at B = 4T. We have observed another FCI with C = -6/5 at v = 12/5, supported by the Streda formula and anomalous Hall effects induced time reversal symmetry breakings. In addition, we observe Chern insulators with C = 1 and 2 at even-denominator fractional filling v = 1/2 and 3/2, respectively, and strikingly, the signatures of anomalous Hall crystal phases with high Chern numbers (C > 1) that develops continuously from v = 1 to the even-denominator v = 3/2 at zero magnetic fields in device D1 and D3. Our results demonstrate the tRTBG, which can be naturally extended to other twisted graphene moire superlattices based on rhombohedral graphene multilayers, as a novel platform for hosting unconventional high Chern number correlated topology in the ultra-strong correlated regime that is beyond the paradigm of the fractional phases with C < 1.