Fluctuating magnetism and Pomeranchuk effect in multilayer graphene
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arXiv
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| Main Authors: | , , , , , , , , , , , |
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| Format: | Preprint |
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2024
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| _version_ | 1866909541577261056 |
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| author | Holleis, Ludwig Xie, Tian Xu, Siyuan Zhou, Haoxin Patterson, Caitlin L. Panigrahi, Archisman Taniguchi, Takashi Watanabe, Kenji Levitov, Leonid S. Jin, Chenhao Berg, Erez Young, Andrea F. |
| author_facet | Holleis, Ludwig Xie, Tian Xu, Siyuan Zhou, Haoxin Patterson, Caitlin L. Panigrahi, Archisman Taniguchi, Takashi Watanabe, Kenji Levitov, Leonid S. Jin, Chenhao Berg, Erez Young, Andrea F. |
| contents | Magnetism typically arises from the effect of exchange interactions on highly localized fermionic wave functions in f- and d-atomic orbitals. In rhombohedral multilayer graphene (RMG), in contrast, magnetism-manifesting as spontaneous polarization into one or more spin and valley flavors[1-7]-originates from itinerant electrons near a Van Hove singularity. Here, we show experimentally that the electronic entropy in this system shows signatures typically associated with disordered local magnetic moments, unexpected for electrons in a fully itinerant metal. Specifically, we find a contribution $Δ$ S $\approx$ 1k$_B$/charge carrier that onsets at the Curie temperature and survives over one order of magnitude in temperature. First order phase transitions show an isospin `Pomeranchuk effect' in which the fluctuating moment phase is entropically favored over the nearby symmetric Fermi liquid[8, 9]. Our results imply that despite the itinerant nature of the electron wave functions, the spin- and valley polarization of individual electrons are decoupled, a phenomenon typically associated with localized moments, as happens, for example, in solid 3He[10]. Transport measurements, surprisingly, show a finite temperature resistance minimum within 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. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2407_13763 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Fluctuating magnetism and Pomeranchuk effect in multilayer graphene Holleis, Ludwig Xie, Tian Xu, Siyuan Zhou, Haoxin Patterson, Caitlin L. Panigrahi, Archisman Taniguchi, Takashi Watanabe, Kenji Levitov, Leonid S. Jin, Chenhao Berg, Erez Young, Andrea F. Strongly Correlated Electrons Mesoscale and Nanoscale Physics Materials Science Magnetism typically arises from the effect of exchange interactions on highly localized fermionic wave functions in f- and d-atomic orbitals. In rhombohedral multilayer graphene (RMG), in contrast, magnetism-manifesting as spontaneous polarization into one or more spin and valley flavors[1-7]-originates from itinerant electrons near a Van Hove singularity. Here, we show experimentally that the electronic entropy in this system shows signatures typically associated with disordered local magnetic moments, unexpected for electrons in a fully itinerant metal. Specifically, we find a contribution $Δ$ S $\approx$ 1k$_B$/charge carrier that onsets at the Curie temperature and survives over one order of magnitude in temperature. First order phase transitions show an isospin `Pomeranchuk effect' in which the fluctuating moment phase is entropically favored over the nearby symmetric Fermi liquid[8, 9]. Our results imply that despite the itinerant nature of the electron wave functions, the spin- and valley polarization of individual electrons are decoupled, a phenomenon typically associated with localized moments, as happens, for example, in solid 3He[10]. Transport measurements, surprisingly, show a finite temperature resistance minimum within 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. |
| title | Fluctuating magnetism and Pomeranchuk effect in multilayer graphene |
| topic | Strongly Correlated Electrons Mesoscale and Nanoscale Physics Materials Science |
| url | https://arxiv.org/abs/2407.13763 |