Nature. 2023 Aug 17. doi: 10.1038/s41586-023-06536-0. Online ahead of print.
ABSTRACT
The integer quantum anomalous Hall (QAH) effect is a lattice analog of the quantum Hall effect at zero magnetic field1-3. This striking phenomenon occurs in systems with topologically nontrivial bands and spontaneous time-reversal symmetry breaking. Discovery of its fractional counterpart in the presence of strong electron correlations, i.e., the fractional quantum anomalous Hall (FQAH) effect4-7, would open a new chapter in condensed matter physics. Here, we report direct observation of both integer and fractional QAH effects in electrical measurements on twisted bilayer MoTe2. At zero magnetic field, near filling factor [Formula: see text] (one hole per moiré unit cell) we see an integer QAH plateau in the Hall resistance Rxy quantized to [Formula: see text] while longitudinal resistance Rxx vanishes. Remarkably, at [Formula: see text] and [Formula: see text] we see plateau features in Rxy at [Formula: see text] and [Formula: see text], respectively, while Rxx remains small. All features shift linearly versus applied magnetic field with slopes matching the corresponding Chern numbers [Formula: see text], [Formula: see text], and [Formula: see text], precisely as expected for integer and fractional QAH states. Additionally, at zero magnetic field, Rxy is approximately 2[Formula: see text] near half filling ([Formula: see text]) and varies linearly as [Formula: see text] is tuned. This behavior resembles that of the composite Fermi liquid in the half-filled lowest Landau level of a two-dimensional electron gas at high magnetic field8-14. Direct observation of the FQAH and associated effects paves the way for researching charge fractionalization and anyonic statistics at zero magnetic field.
PMID:37591304 | DOI:10.1038/s41586-023-06536-0
