Cryo-Near-Field Photovoltage Microscopy of Heavy-Fermion Twisted Symmetric Trilayer Graphene

Cryo-Near-Field Photovoltage Microscopy of Heavy-Fermion Twisted Symmetric Trilayer Graphene | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Cryo-Near-Field Photovoltage Microscopy of Heavy-Fermion Twisted Symmetric Trilayer Graphene Frank Koppens, Sergi Batlle-Porro, Petr Stepanov, Dumitru Calugaru, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3968061/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 20 Nov, 2025 Read the published version in Nature Physics → Version 1 posted You are reading this latest preprint version Abstract Ever since the initial experimental observation of correlated insulators and superconductivity in the flat Dirac bands of magic angle twisted bilayer graphene, a search for the microscopic description that explains its strong electronic interactions has begun. While the seemingly disagreeing electronic transport and scanning tunneling microscopy experiments suggest a dichotomy between local and extended electronic orbitals, definitive experimental evidence merging the two patterns together has been much sought after. Here, we report on the local photothermoelectric measurements in the flat electronic bands of twisted symmetric trilayer graphene (TSTG). We use a cryogenic scanning near-field optical microscope with an oscillating atomic force microscopy (AFM) tip irradiated by the infrared photons to create a nanoscopic hot spot in the planar samples, which generates a photocurrent that we probe globally. We observe a breakdown of the non-interacting Mott formalism at low temperatures (∼10K), signaling the importance of the electronic interactions. Our measurements reveal an overall negative offset of the Seebeck coefficient and significant peaks of the local photovoltage values at all positive integer fillings of the TSTG's moiré superlattice, further indicating a substantial deviation from the classical two-band semiconductor Seebeck response. We explain these observations using the interacting topological heavy-fermion model. In addition, our data reveal a spatial variation of the relative interaction strength dependent on the measured local twist angle (1.2° - 1.6°). Our findings provide experimental evidence of heavy fermion behaviour in the topological flat bands of moiré graphene and epitomize an avenue to apply local thermoelectric measurements to other strongly correlated materials in the disorder-free limit. Physical sciences/Physics/Condensed-matter physics/Electronic properties and materials Physical sciences/Physics/Condensed-matter physics/Topological matter Physical sciences/Physics/Electronics, photonics and device physics Physical sciences/Nanoscience and technology/Graphene Full Text Additional Declarations There is NO Competing Interest. Supplementary Files CryoNFPVinTSTGSI.pdf Supplementary materials Cite Share Download PDF Status: Published Journal Publication published 20 Nov, 2025 Read the published version in Nature Physics → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3968061","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":282613569,"identity":"c7506d98-627a-4368-9124-47d886fc99b3","order_by":0,"name":"Frank Koppens","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4klEQVRIiWNgGAWjYBAC9gYGBsYGhgQot0ICLIIX8BxA0XJGAixCghbGNgYitEgffvZwBkOanLl087GHP+dZyPOwNzA+5sGnhS/N3HADQ46x5Zxj6ca82yQMe3gOMBvj02LPw2Am+YChInHDjRwzacZtEgn2Egls0nht4WH/BtWS/03y5xyJBB6JBPbf+LXwmEkCHQayhU2CtwGshY2ZgJYyyRkGaSC/mEnzHAP55WCz5Bz8Dtsm2VORDAqxZ5I/auqAIdZ88MMbPFogwACIJOA8YDwRBZC0jIJRMApGwShABQDDQkH4yc+iQQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0001-9764-6120","institution":"ICFO-The Institute of Photonic Sciences, The Barcelona Institute of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Frank","middleName":"","lastName":"Koppens","suffix":""},{"id":282613570,"identity":"e5b31bb5-6e18-4d4a-9fae-3117c2d0753b","order_by":1,"name":"Sergi Batlle-Porro","email":"","orcid":"https://orcid.org/0000-0001-9663-8268","institution":"ICFO - The Institute of Photonic Sciences","correspondingAuthor":false,"prefix":"","firstName":"Sergi","middleName":"","lastName":"Batlle-Porro","suffix":""},{"id":282613571,"identity":"274c3079-c925-4afb-88d2-08f70964f62d","order_by":2,"name":"Petr Stepanov","email":"","orcid":"","institution":"Institut de Ciències Fotòniques","correspondingAuthor":false,"prefix":"","firstName":"Petr","middleName":"","lastName":"Stepanov","suffix":""},{"id":282613572,"identity":"4327bda5-6957-46c5-8308-5ced15c47dbf","order_by":3,"name":"Dumitru Calugaru","email":"","orcid":"https://orcid.org/0000-0002-5897-9878","institution":"Princeton University","correspondingAuthor":false,"prefix":"","firstName":"Dumitru","middleName":"","lastName":"Calugaru","suffix":""},{"id":282613573,"identity":"3dc0e315-4053-4013-b574-7b0d1e1af07a","order_by":4,"name":"Haoyu Hu","email":"","orcid":"","institution":"Donostia International Physics Center (DIPC), Paseo Manuel de Lardizábal. 20018, San Sebastián, Spain","correspondingAuthor":false,"prefix":"","firstName":"Haoyu","middleName":"","lastName":"Hu","suffix":""},{"id":282613574,"identity":"f09104cc-ded3-4415-99a4-88311d5ee33f","order_by":5,"name":"Roshan Krishna Kumar","email":"","orcid":"https://orcid.org/0000-0003-0857-4466","institution":"ICFO - The Institute of Photonic Sciences","correspondingAuthor":false,"prefix":"","firstName":"Roshan","middleName":"Krishna","lastName":"Kumar","suffix":""},{"id":282613575,"identity":"72590d48-530c-41d3-a5f5-803f9fe840e2","order_by":6,"name":"Niels Hesp","email":"","orcid":"https://orcid.org/0000-0001-8111-9780","institution":"ICFO - The Institute of Photonic Sciences","correspondingAuthor":false,"prefix":"","firstName":"Niels","middleName":"","lastName":"Hesp","suffix":""},{"id":282613576,"identity":"e5d128af-e1ea-4590-b009-7326a050be9b","order_by":7,"name":"B. 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