Heavy fermions, mass renormalization, and local moments in magic-angle twisted bilayer graphene via planar tunneling spectroscopy

Heavy fermions, mass renormalization, and local moments in magic-angle twisted bilayer graphene via planar tunneling spectroscopy | 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 Physical Sciences - Article Heavy fermions, mass renormalization, and local moments in magic-angle twisted bilayer graphene via planar tunneling spectroscopy Eva Andrei, Zhenyuan Zhang, Shuang Wu, Dumitru Calugaru, Haoyu Hu, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6349908/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Topological heavy fermion models[1-5] describe the flat bands in magic-angle twisted bilayer graphene (MATBG) as arising from the hybridization between localized flat-band orbitals ( f -electrons) and nearly-free conduction bands ( c -electrons). The interplay between these f -electrons and c -electrons is theorized to give rise to emergent phenomena, including unconventional superconductivity[6-8], non-Fermi liquid behavior[9-13], and topologically nontrivial phases[12, 14, 15]. However, the fundamental properties of f - and c -electrons, such as their respective heavy and light effective mass and their properties under strain, need experimental verification. Here we report on the electronic inverse compressibility, effective mass, and entropy of MATBG, obtained from planar tunneling spectroscopy. Our results include the observation of electron mass renormalization, found to be consistent with the topological heavy fermion model prediction of heavy charge-one excitations away from integer fillings. Importantly, we present entropic evidence for 4-fold and 8-fold degenerate isospin local moment states emerging at temperatures of 10K and 20K, respectively, consistent with the entropy of 8 heavy-fermions flavors energetically split by the sample strain. Physical sciences/Nanoscience and technology/Graphene Physical sciences/Materials science/Condensed-matter physics Full Text Additional Declarations There is NO Competing Interest. Supplementary Files SIheavyfermionMATBGcomp.pdf Supplementary information Cite Share Download PDF Status: Under Review 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-6349908","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":440042268,"identity":"6cbcd184-ee79-404f-beee-3d41892270a5","order_by":0,"name":"Eva Andrei","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0002-2516-2749","institution":"Rutgers, The State University of New Jersey","correspondingAuthor":true,"prefix":"","firstName":"Eva","middleName":"","lastName":"Andrei","suffix":""},{"id":440042269,"identity":"7430e3fd-90d9-4835-9eaa-82b968c03fae","order_by":1,"name":"Zhenyuan Zhang","email":"","orcid":"","institution":"Rutgers, The State University of New Jersey","correspondingAuthor":false,"prefix":"","firstName":"Zhenyuan","middleName":"","lastName":"Zhang","suffix":""},{"id":440042270,"identity":"70c84e75-0403-4a86-a0dd-65f5bb841b88","order_by":2,"name":"Shuang Wu","email":"","orcid":"","institution":"Rutgers, The State University of New Jersey","correspondingAuthor":false,"prefix":"","firstName":"Shuang","middleName":"","lastName":"Wu","suffix":""},{"id":440042271,"identity":"63aeada7-b755-4377-86e1-279332890f94","order_by":3,"name":"Dumitru Calugaru","email":"","orcid":"https://orcid.org/0000-0002-5897-9878","institution":"Rudolf Peierls Centre for Theoretical Physics, University of Oxford","correspondingAuthor":false,"prefix":"","firstName":"Dumitru","middleName":"","lastName":"Calugaru","suffix":""},{"id":440042272,"identity":"55b5e50a-1b8a-404f-81a9-a854729d3d82","order_by":4,"name":"Haoyu Hu","email":"","orcid":"https://orcid.org/0000-0002-3787-6634","institution":"Donostia International Physics Center (DIPC), Paseo Manuel de Lardizábal. 20018, San Sebastián, Spain","correspondingAuthor":false,"prefix":"","firstName":"Haoyu","middleName":"","lastName":"Hu","suffix":""},{"id":440042273,"identity":"c388dbb3-99be-4ddd-8418-6cb6585c3fbc","order_by":5,"name":"Takashi Taniguchi","email":"","orcid":"https://orcid.org/0000-0002-1467-3105","institution":"National Institute for Materials Science Tsukuba Ibaraki","correspondingAuthor":false,"prefix":"","firstName":"Takashi","middleName":"","lastName":"Taniguchi","suffix":""},{"id":440042274,"identity":"b7edaa9e-2a62-43ad-a49d-a3ea4119747f","order_by":6,"name":"Kenji Watanabe","email":"","orcid":"https://orcid.org/0000-0003-3701-8119","institution":"National Institute for Materials Science","correspondingAuthor":false,"prefix":"","firstName":"Kenji","middleName":"","lastName":"Watanabe","suffix":""},{"id":440042275,"identity":"6a82118c-3ad8-4df4-8b89-90760f1319f6","order_by":7,"name":"B. Andrei Bernevig","email":"","orcid":"https://orcid.org/0000-0001-6337-4024","institution":"Princeton University","correspondingAuthor":false,"prefix":"","firstName":"B.","middleName":"Andrei","lastName":"Bernevig","suffix":""}],"badges":[],"createdAt":"2025-04-01 06:10:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6349908/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6349908/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":94672250,"identity":"7a969f70-7cab-4dd9-81c4-2a9d28486c3d","added_by":"auto","created_at":"2025-10-29 13:40:01","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2479687,"visible":true,"origin":"","legend":"","description":"","filename":"MS23325.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6349908/v1_covered_0b602241-6dbb-4ac7-9c20-dcf9653a67f6.pdf"},{"id":80198742,"identity":"54566148-9167-4314-9aa9-6776aac27fab","added_by":"auto","created_at":"2025-04-09 06:21:50","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":16362109,"visible":true,"origin":"","legend":"Supplementary information","description":"","filename":"SIheavyfermionMATBGcomp.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6349908/v1/7213276f211731b71a712329.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Heavy fermions, mass renormalization, and local moments in magic-angle twisted bilayer graphene via planar tunneling spectroscopy","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6349908/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6349908/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTopological heavy fermion models[1-5] describe the flat bands in magic-angle twisted bilayer graphene (MATBG) as arising from the hybridization between localized flat-band orbitals (\u003cem\u003ef\u003c/em\u003e-electrons) and nearly-free conduction bands (\u003cem\u003ec\u003c/em\u003e-electrons). The interplay between these \u003cem\u003ef\u003c/em\u003e-electrons and \u003cem\u003ec\u003c/em\u003e-electrons is theorized to give rise to emergent phenomena, including unconventional superconductivity[6-8], non-Fermi liquid behavior[9-13], and topologically nontrivial phases[12, 14, 15]. However, the fundamental properties of \u003cem\u003ef\u003c/em\u003e- and \u003cem\u003ec\u003c/em\u003e-electrons, such as their respective heavy and light effective mass and their properties under strain, need experimental verification. Here we report on the electronic inverse compressibility, effective mass, and entropy of MATBG, obtained from planar tunneling spectroscopy. Our results include the observation of electron mass renormalization, found to be consistent with the topological heavy fermion model prediction of heavy charge-one excitations away from integer fillings. Importantly, we present entropic evidence for 4-fold and 8-fold degenerate isospin local moment states emerging at temperatures of 10K and 20K, respectively, consistent with the entropy of 8 heavy-fermions flavors energetically split by the sample strain.\u003c/p\u003e","manuscriptTitle":"Heavy fermions, mass renormalization, and local moments in magic-angle twisted bilayer graphene via planar tunneling spectroscopy","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-09 06:21:44","doi":"10.21203/rs.3.rs-6349908/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"320e042e-da9f-4d07-8260-3bcfce6f7849","owner":[],"postedDate":"April 9th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":46845921,"name":"Physical sciences/Nanoscience and technology/Graphene"},{"id":46845922,"name":"Physical sciences/Materials science/Condensed-matter physics"}],"tags":[],"updatedAt":"2026-03-05T20:50:20+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-09 06:21:44","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6349908","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6349908","identity":"rs-6349908","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}