Observation of fractionally quantized anomalous Hall effect

• Published in: Nature (London) Vol. 622; no. 7981; pp. 74 - 79
• Main Authors: Park, Heonjoon, Cai, Jiaqi, Anderson, Eric, Zhang, Yinong, Zhu, Jiayi, Liu, Xiaoyu, Wang, Chong, Holtzmann, William, Hu, Chaowei, Liu, Zhaoyu, Taniguchi, Takashi, Watanabe, Kenji, Chu, Jiun-Haw, Cao, Ting, Fu, Liang, Yao, Wang, Chang, Cui-Zu, Cobden, David, Xiao, Di, Xu, Xiaodong
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 05.10.2023; Nature Publishing Group
• Subjects: 140/125; 142/126; 639/766/119/2792/4128; 639/766/119/2793; 639/766/119/2794; 639/766/119/2795; Broken symmetry; Coagulation factors; Condensed matter physics; Electric fields; Electrical measurement; Electromagnetism; Electron gas; Electrons; Factor V; Fermi liquids; Hall effect; Humanities and Social Sciences; Integers; Magnetic fields; multidisciplinary; Phase transitions; Quantum Hall effect; Science; Science & Technology - Other Topics; Science (multidisciplinary); Symmetry; Unit cell
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/s41586-023-06536-0

The integer quantum anomalous Hall (QAH) effect is a lattice analogue of the quantum Hall effect at zero magnetic field 1 – 3 . This phenomenon occurs in systems with topologically non-trivial bands and spontaneous time-reversal symmetry breaking. Discovery of its fractional counterpart in the presence of strong electron correlations, that is, the fractional QAH effect 4 – 7 , would open a new chapter in condensed matter physics. Here we report the direct observation of both integer and fractional QAH effects in electrical measurements on twisted bilayer MoTe 2 . At zero magnetic field, near filling factor ν  = −1 (one hole per moiré unit cell), we see an integer QAH plateau in the Hall resistance R xy quantized to h / e 2  ± 0.1%, whereas the longitudinal resistance R xx vanishes. Remarkably, at ν   =  −2/3 and −3/5, we see plateau features in R xy at 3 2 h / e 2 ± 1 % and 5 3 h / e 2 ± 3 % , respectively, whereas R xx remains small. All features shift linearly versus applied magnetic field with slopes matching the corresponding Chern numbers −1, −2/3 and −3/5, precisely as expected for integer and fractional QAH states. Additionally, at zero magnetic field, R xy is approximately 2 h / e 2 near half-filling ( ν   = −1/2) and varies linearly as ν   is tuned. This behaviour resembles that of the composite Fermi liquid in the half-filled lowest Landau level of a two-dimensional electron gas at high magnetic field 8 – 14 . Direct observation of the fractional QAH and associated effects enables research in charge fractionalization and anyonic statistics at zero magnetic field. Transport measurements in twisted bilayer MoTe 2 reveal quantized Hall resistance plateaus and composite Fermi liquid-like behaviour under zero magnetic field, constituting a direct observation of integer and fractional quantum anomalous Hall effects.