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DOE OSTI · 3365460

Fractional quantization in insulators from Hall to Chern

Bernevig, B. A. [Princeton University, NJ (United States); Donostia International Physics Center (Spain); IKERBASQUE, Basque Foundation for Science, Bilbao (Spain)] (ORCID:0000000163374024)·Fu, Liang [Massachusetts Institute of Technology, Cambridge, MA (United States)] (ORCID:0000000288031017)·Ju, Long [Massachusetts Institute of Technology, Cambridge, MA (United States)] (ORCID:0000000246911315)·MacDonald, A. H. [University of Texas at Austin, TX (United States)] (ORCID:0000000335613379)·Mak, Kin Fai [Max Planck Institute for the Structure and Dynamics of Matter, Hamburg (Germany); Cornell University, Ithaca, NY (United States); Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY (United States)] (ORCID:000000025768199X)·Shan, Jie [Max Planck Institute for the Structure and Dynamics of Matter, Hamburg (Germany); Cornell University, Ithaca, NY (United States); Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY (United States)] (ORCID:0000000312709386)
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Abstract

The discovery of the integer and fractional quantum Hall effects naturally prompted the question of whether these effects can be realized without a magnetic field. Answering this is fundamentally important and requires a synthesis of the concepts of band topology, quantum geometry and electronic correlations. Here we summarize the basic concepts of both fractional Chern and fractional topological insulators and illustrate them with the theoretical lattice models that support the flat Chern bands in which the states were first predicted. We then examine their experimental realizations in twisted bilayer transition metal dichalcogenides and moiré rhombohedral few-layer graphene. Here, we also discuss the future challenges and opportunities in this research field.

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Bernevig, B. A. [Princeton University, NJ (United States); Donostia International Physics Center (Spain); IKERBASQUE, Basque Foundation for Science, Bilbao (Spain)] (ORCID:0000000163374024), Fu, Liang [Massachusetts Institute of Technology, Cambridge, MA (United States)] (ORCID:0000000288031017), Ju, Long [Massachusetts Institute of Technology, Cambridge, MA (United States)] (ORCID:0000000246911315), MacDonald, A. H. [University of Texas at Austin, TX (United States)] (ORCID:0000000335613379), Mak, Kin Fai [Max Planck Institute for the Structure and Dynamics of Matter, Hamburg (Germany); Cornell University, Ithaca, NY (United States); Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY (United States)] (ORCID:000000025768199X), Shan, Jie [Max Planck Institute for the Structure and Dynamics of Matter, Hamburg (Germany); Cornell University, Ithaca, NY (United States); Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY (United States)] (ORCID:0000000312709386). 2025-11-07. Fractional quantization in insulators from Hall to Chern. https://doi.org/10.1038/s41567-025-03072-8

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DOE OSTI2026

Signatures of fractional charges via anyon–trions in twisted MoTe 2

Fractionalization of the electron charge e is one of the most striking phenomena arising from strong electron–electron interactions. A celebrated example is the emergence of anyons with fractional charges in fractional quantum Hall effect (FQHE) states. Recently, zero-field fractional Chern insulators (FCIs), lattice analogues of the FQHE states that form without Landau levels, have been realized. FCIs provide a unique platform to investigate anyons, yet their detection remains a challenge. Here we report the observation of anyon–trions, a new type of excitonic complex formed by binding a trion with a fractional charge in twisted MoTe 2 bilayers. Photoluminescence spectroscopy of quantum-confined excitons reveals emergent peaks that appear only within slightly doped FCI states. The new spectral features are red-shifted relative to the trions in undoped FCIs, but share the same electric field, temperature and magnetic field dependence. These observations suggest their origin as trions binding with elementary quasi-particles, that is, anyon–trions. Crucially, the ratio of binding energies between the anyon–trions in the −2/3 and −3/5 FCI states matches the expected fractional charge ratio of e/3 to e/5. This provides strong evidence for fractional charges in FCI—an essential property of anyons. Our results address a fundamental question in FCI physics and establish trion spectroscopy as a powerful probe of fractionally charged excitations, complementary to transport- and tunnelling-based approaches.

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