Thermopower probing emergent local moments in magic-angle twisted bilayer graphene

Thermopower probing emergent local moments in magic-angle twisted bilayer 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 Physical Sciences - Article Thermopower probing emergent local moments in magic-angle twisted bilayer graphene Anindya Das, Ayan Ghosh, Souvik Chakraborty, Ranit Dutta, Adhip Agarwala, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4118348/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 31 Mar, 2025 Read the published version in Nature Physics → Version 1 posted You are reading this latest preprint version Abstract Recent experiments on magic-angle twisted bilayer graphene (MATBLG) indicate an unusual coexistence of heavy 1-6 and light 7-10 fermions. Yet, these experiments lack direct evidence of the existence of local moments arising from the flatband, a key component of heavy-fermion physics 11-16 . Utilizing thermopower as a sensitive probe for measuring entropy 17 , we unveil the presence of local moments through their impact on entropy. Remarkably, in addition to sign changes at the Dirac point (ν = 0) and full band filling (ν = ±4), the thermopower demonstrates additional sign changes at the location, ν cross ∼ ±1, which does not vary with temperature from 5K to ∼ 60K. This observation cannot be explained solely from the contributions of band fermions; instead, our data is consistent with the dominant contribution arising from the entropy of the localized moments. To validate our claim, we have investigated the effect of magnetic field (B) on the thermopower, both B ∥ and B ⊥ . Our results show a 30% and 50% reduction, respectively, and can be attributed to the partial polarization of the local moments (spin/valley), resulting in decreased entropy. Our thermopower results highlight the contribution from local moments arising from flatbands, distinct from the band contributions to the resistivity in MATBLG. Physical sciences/Physics/Condensed-matter physics/Electronic properties and materials Physical sciences/Nanoscience and technology/Graphene/Electronic properties and devices Full Text Additional Declarations There is NO Competing Interest. Supplementary Files ThermopowerHeavyFermionSUPPLIMENTARYNature.pdf Thermopower probing emergent local moments in magic-angle twisted bilayer graphene ExtendedDATAcompressed.pdf Extended Data Cite Share Download PDF Status: Published Journal Publication published 31 Mar, 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. 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-4118348","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":281082224,"identity":"d6bccd84-ba12-4bb4-aa5b-4d2dc595eb69","order_by":0,"name":"Anindya 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Yet, these experiments lack direct evidence of the existence of local moments arising from the flatband, a key component of heavy-fermion physics \u003csup\u003e11-16\u003c/sup\u003e. Utilizing thermopower as a sensitive probe for measuring entropy \u003csup\u003e17\u003c/sup\u003e, we unveil the presence of local moments through their impact on entropy. Remarkably, in addition to sign changes at the Dirac point (ν = 0) and full band filling (ν = ±4), the thermopower demonstrates additional sign changes at the location, ν\u003csub\u003ecross\u003c/sub\u003e ∼ ±1, which does not vary with temperature from 5K to ∼ 60K. This observation cannot be explained solely from the contributions of band fermions; instead, our data is consistent with the dominant contribution arising from the entropy of the localized moments. To validate our claim, we have investigated the effect of magnetic field (B) on the thermopower, both B\u003csub\u003e∥\u003c/sub\u003e and B\u003csub\u003e⊥\u003c/sub\u003e. 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