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Magnetism typically arises from the effect of exchange interactions on highly localized fermionic wavefunctions in f- and d-atomic orbitals. By contrast, in rhombohedral multilayer graphene (RMG), magnetism—manifesting as spontaneous polarization into one or more spin and valley flavours—originates from itinerant electrons near a Van Hove singularity. Here we show experimentally that the electronic entropy in this system indicates signatures typically associated with disordered local magnetic moments, unexpected for electrons in a fully itinerant metal. Specifically, we find a contribution ΔS ≈ 1 kB per charge carrier that begins at the Curie temperature and survives more than one order of magnitude in temperature. First-order phase transitions show an isospin ‘Pomeranchuk effect’ in which the fluctuating moment phase is entropically favoured over the nearby symmetric Fermi liquid. Our results imply that, despite the itinerant nature of the electron wavefunctions, the spin and valley polarization of individual electrons is decoupled, a phenomenon typically associated with localized moments, as happens, for example, in solid 3He. Transport measurements, surprisingly, show a finite-temperature resistance minimum in the fluctuating moment regime, which we attribute to the interplay of fluctuating magnetic moments and electron–phonon scattering. Our results highlight the universality of soft isospin modes to two-dimensional flat-band systems.

権利情報:

• Creative Commons BY-NC-SA Attribution-NonCommercial-ShareAlike 4.0 International
  

キーワード: Rhombohedral multilayer graphene, Magnetism, Van Hove singularity

刊行年月日: 2025-04-10

出版者: Springer Science and Business Media LLC

掲載誌:

• Nature (ISSN: 00280836) vol. 640 issue. 8058 p. 355-360

研究助成金:

原稿種別: 著者最終稿 (Accepted manuscript)

MDR DOI:

公開URL: https://doi.org/10.1038/s41586-025-08725-5

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更新時刻: 2026-07-28 13:35:57 +0900

MDRでの公開時刻: 2026-07-28 16:27:18 +0900