Heonjoon (Joon) Park

All Publications

• Observation of dissipationless fractional Chern insulator NATURE PHYSICS Park, H., Li, W., Hu, C., Beach, C., Goncalves, M., Mendez-Valderrama, J., Herzog-Arbeitman, J., Taniguchi, T., Watanabe, K., Cobden, D., Fu, L., Bernevig, B., Regnault, N., Chu, J., Xiao, D., Xu, X. 2026

  View details for DOI 10.1038/s41567-025-03167-2

  View details for Web of Science ID 001674739100001

• Local probe of bulk and edge states in a fractional Chern insulator. Nature Ji, Z., Park, H., Barber, M. E., Hu, C., Watanabe, K., Taniguchi, T., Chu, J. H., Xu, X., Shen, Z. X. 2024; 635 (8039): 578-583

  Abstract

  The fractional quantum Hall effect is a key example of topological quantum many-body phenomena, arising from the interplay between strong electron correlation, topological order and time-reversal symmetry breaking. Recently, a lattice analogue of the fractional quantum Hall effect at zero magnetic field has been observed, confirming the existence of a zero-field fractional Chern insulator (FCI). Despite this, the bulk-edge correspondence-a hallmark of a FCI featuring an insulating bulk with conductive edges-has not been directly observed. In fact, this correspondence has not been visualized in any system for fractional states owing to experimental challenges. Here we report the imaging of FCI edge states in twisted MoTe2 (t-MoTe2) using microwave impedance microscopy1. By tuning the carrier density, we observe the system evolving between metallic and FCI states, the latter of which exhibits insulating bulk and conductive edges, as expected from the bulk-boundary correspondence. Further analysis suggests the composite nature of the FCI edge states. We also observe the evolution of edge states across the topological phase transition as a function of interlayer electric field and reveal exciting prospects of neighbouring domains with different fractional orders. These findings pave the way for research into topologically protected one-dimensional interfaces between various anyonic states at zero magnetic field, such as gapped one-dimensional symmetry-protected phases with non-zero topological entanglement entropy, Halperin-Laughlin interfaces and the creation of non-abelian anyons.

  View details for DOI 10.1038/s41586-024-08092-7

  View details for PubMedID 39567787

  View details for PubMedCentralID 11464376

• Observation of fractionally quantized anomalous Hall effect. Nature Park, H., Cai, J., Anderson, E., Zhang, Y., Zhu, J., Liu, X., Wang, C., Holtzmann, W., Hu, C., Liu, Z., Taniguchi, T., Watanabe, K., Chu, J. H., Cao, T., Fu, L., Yao, W., Chang, C. Z., Cobden, D., Xiao, D., Xu, X. 2023; 622 (7981): 74-79

  Abstract

  The integer quantum anomalous Hall (QAH) effect is a lattice analogue of the quantum Hall effect at zero magnetic field1-3. 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 effect4-7, 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 MoTe2. 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 Rxy quantized to h/e2 ± 0.1%, whereas the longitudinal resistance Rxx vanishes. Remarkably, at ν  =  -2/3 and -3/5, we see plateau features in Rxy at [Formula: see text] and [Formula: see text], respectively, whereas Rxx 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, Rxy is approximately 2h/e2 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 field8-14. Direct observation of the fractional QAH and associated effects enables research in charge fractionalization and anyonic statistics at zero magnetic field.

  View details for DOI 10.1038/s41586-023-06536-0

  View details for PubMedID 37591304

  View details for PubMedCentralID 10533412

• Optical control of integer and fractional Chern insulators NATURE Holtzmann, W., Li, W., Anderson, E., Cai, J., Park, H., Hu, C., Taniguchi, T., Watanabe, K., Chu, J., Xiao, D., Cao, T., Xu, X. 2026; 649 (8099): 1147-1152

  Abstract

  Optical control of topology, particularly in the presence of electron correlations, is an interesting topic with broad scientific and technological impact1-4. Twisted MoTe2 bilayer (tMoTe2) is a zero-field fractional Chern insulator (FCI)5-10, exhibiting the fractionally quantized anomalous Hall effect11-14. As the chirality of the edge states and sign of the Chern number are determined by the underlying ferromagnetic polarization15,16, manipulation of ferromagnetism would realize control of the Chern insulator (CI)/FCI states. Here we demonstrate control of ferromagnetic polarization, and thus the CI and FCI states, by circularly polarized optical pumping in tMoTe2. At low excitation power, we achieve on-demand preparation of ferromagnetic polarization by optical training, that is, electrically tuning the system from non-ferromagnetic to desirable ferromagnetic states under helicity-selective optical pumping. With increased excitation power, we further realize direct optical switching of ferromagnetic polarization at a temperature far below the Curie temperature17,18. Both optical training and direct switching are most effective near CI and FCI states, which we attribute to a gap-enhanced valley polarization of optically pumped holes. The magnetization can be dynamically switched by modulating the helicity of optical excitation. Spatially resolved measurements further demonstrate optical writing of ferromagnetic, and thus CI (or FCI) domains. Our work realizes precise optical control of a topological quantum many-body system with potential applications in topological spintronics, quantum memories and creation of exotic edge states by programmable patterning of integer and fractionally quantized anomalous Hall domains4,19.

  View details for DOI 10.1038/s41586-025-09777-3

  View details for Web of Science ID 001684101100031

  View details for PubMedID 41606148

  View details for PubMedCentralID 5529060

• Universal Magnetic Phases in Twisted Bilayer MoTe₂ NANO LETTERS Li, W., Redekop, E., Wang Beach, C., Zhang, C., Zhang, X., Liu, X., Holtzmann, W., Hu, C., Anderson, E., Park, H., Taniguchi, T., Watanabe, K., Chu, J., Fu, L., Cao, T., Xiao, D., Young, A. F., Xu, X. 2025: 18044-18050

  Abstract

  Twisted bilayer MoTe2 (tMoTe2) has emerged as a robust platform for exploring correlated topological phases, yet the evolution of its magnetism and topology with twist angle remains an open question. Here, we systematically map the magnetic phase diagram of tMoTe2 by using local optical spectroscopy and scanning nanoSQUID-on-tip magnetometry. We identify spontaneous ferromagnetism at filling factors ν = -1 and -3 across twist angles from 2.1° to 3.7°, revealing a universal, twist-angle-insensitive ferromagnetic phase. At 2.1°, we further observe robust ferromagnetism at ν = -5, absent at larger twist angles. Temperature-dependent measurements reveal a contrasting twist-angle dependence of the Curie temperatures between ν = -1 and -3, indicating a distinct interplay between the exchange interactions and bandwidth for the two Chern bands. Despite broken time-reversal symmetry, no topological gap is detected at ν = -3. Our results establish a global framework for understanding and controlling magnetic order in tMoTe2.

  View details for DOI 10.1021/acs.nanolett.5c04751

  View details for Web of Science ID 001644281800001

  View details for PubMedID 41413379

• Microscopic signatures of topology in twisted MoTe₂ NATURE PHYSICS Thompson, E., Chu, K., Mesple, F., Zhang, X., Hu, C., Zhao, Y., Park, H., Cai, J., Anderson, E., Watanabe, K., Taniguchi, T., Yang, J., Chu, J., Xu, X., Cao, T., Xiao, D., Yankowitz, M. 2025; 21 (8)

  View details for DOI 10.1038/s41567-025-02877-x

  View details for Web of Science ID 001479670100001

• Ferromagnetism and topology of the higher flat band in a fractional Chern insulator NATURE PHYSICS Park, H., Cai, J., Anderson, E., Zhang, X., Liu, X., Holtzmann, W., Li, W., Wang, C., Hu, C., Zhao, Y., Taniguchi, T., Watanabe, K., Yang, J., Cobden, D., Chu, J., Regnault, N., Bernevig, B., Fu, L., Cao, T., Xiao, D., Xu, X. 2025; 21 (4)

  View details for DOI 10.1038/s41567-025-02804-0

  View details for Web of Science ID 001450723300001

• Frozen non-equilibrium dynamics of exciton Mott insulators in moiré superlattices NATURE MATERIALS Deng, S., Park, H., Reimann, J., Peterson, J. M., Blach, D. D., Sun, M., Yan, T., Sun, D., Taniguchi, T., Watanabe, K., Xu, X., Kennes, D. M., Huang, L. 2025; 24 (4): 527-534

  Abstract

  Moiré superlattices, such as those formed from transition metal dichalcogenide heterostructures, have emerged as an exciting platform for exploring quantum many-body physics. They have the potential to serve as solid-state analogues to ultracold gases for quantum simulations. A key open question is the coherence and dynamics of the quantum phases arising from photoexcited moiré excitons, particularly amid dissipation. Here we use transient photoluminescence and ultrafast reflectance microscopy to image non-equilibrium exciton phase transitions. Counterintuitively, experimental results and theoretical simulations indicate that strong long-range dipolar repulsion freezes the motion of the Mott insulator phase for over 70 ns. In mixed electron-exciton lattices, reduced dipolar interactions lead to diminished freezing dynamics. These findings challenge the prevailing notion that repulsion disperses particles, whereas attraction binds them. The observed phenomenon of frozen dynamics due to strong repulsive interactions is characteristic of highly coherent systems, a feature previously realized exclusively in ultracold gases.

  View details for DOI 10.1038/s41563-025-02135-8

  View details for Web of Science ID 001435526500001

  View details for PubMedID 40033108

  View details for PubMedCentralID 7531884

• Direct magnetic imaging of fractional Chern insulators in twisted MoTe₂ NATURE Redekop, E., Zhang, C., Park, H., Cai, J., Anderson, E., Sheekey, O., Arp, T., Babikyan, G., Salters, S., Watanabe, K., Taniguchi, T., Huber, M. E., Xu, X., Young, A. F. 2024; 635 (8039): 584-589

  Abstract

  Orbital magnetization provides a sensitive probe of topology and interactions, with particularly rich phenomenology in Chern insulators in which the topological edge states carry large equilibrium currents. Here we use a nanoscale superconducting sensor1,2 to map the magnetic fringe fields in twisted bilayers of MoTe2, in which transport3,4 and optical sensing5,6 experiments have revealed the formation of fractional Chern insulator (FCI) states at zero magnetic field. We observe oscillations in the local magnetic field associated with fillings ν = -1, -2/3, -3/5, -4/7 and -5/9 of the first moiré hole band, consistent with the formation of FCIs at these fillings. We determine the local thermodynamic gaps of the most robust FCI state at ν = -2/3, finding -2/3Δ as large as 7 meV. We also characterize sample spatial disorder, which is dominated by both inhomogeneity in the effective unit cell area7 as well as inhomogeneity in the band edge offset and bound dipole moment. Our results highlight both the challenges posed by structural disorder in the study of twisted homobilayer moiré systems and the opportunities afforded by the robust nature of the underlying correlated topological states.

  View details for DOI 10.1038/s41586-024-08153-x

  View details for Web of Science ID 001361300200018

  View details for PubMedID 39567790

  View details for PubMedCentralID 8674130