IDEAS home Printed from https://ideas.repec.org/a/nat/nature/v592y2021i7853d10.1038_s41586-021-03319-3.html
   My bibliography  Save this article

Entropic evidence for a Pomeranchuk effect in magic-angle graphene

Author

Listed:
  • Asaf Rozen

    (Weizmann Institute of Science)

  • Jeong Min Park

    (Massachusetts Institute of Technology)

  • Uri Zondiner

    (Weizmann Institute of Science)

  • Yuan Cao

    (Massachusetts Institute of Technology)

  • Daniel Rodan-Legrain

    (Massachusetts Institute of Technology)

  • Takashi Taniguchi

    (National Institute for Materials Science)

  • Kenji Watanabe

    (National Institute for Materials Science)

  • Yuval Oreg

    (Weizmann Institute of Science)

  • Ady Stern

    (Weizmann Institute of Science)

  • Erez Berg

    (Weizmann Institute of Science)

  • Pablo Jarillo-Herrero

    (Massachusetts Institute of Technology)

  • Shahal Ilani

    (Weizmann Institute of Science)

Abstract

In the 1950s, Pomeranchuk1 predicted that, counterintuitively, liquid 3He may solidify on heating. This effect arises owing to high excess nuclear spin entropy in the solid phase, where the atoms are spatially localized. Here we find that an analogous effect occurs in magic-angle twisted bilayer graphene2–6. Using both local and global electronic entropy measurements, we show that near a filling of one electron per moiré unit cell, there is a marked increase in the electronic entropy to about 1kB per unit cell (kB is the Boltzmann constant). This large excess entropy is quenched by an in-plane magnetic field, pointing to its magnetic origin. A sharp drop in the compressibility as a function of the electron density, associated with a reset of the Fermi level back to the vicinity of the Dirac point, marks a clear boundary between two phases. We map this jump as a function of electron density, temperature and magnetic field. This reveals a phase diagram that is consistent with a Pomeranchuk-like temperature- and field-driven transition from a low-entropy electronic liquid to a high-entropy correlated state with nearly free magnetic moments. The correlated state features an unusual combination of seemingly contradictory properties, some associated with itinerant electrons—such as the absence of a thermodynamic gap, metallicity and a Dirac-like compressibility—and others associated with localized moments, such as a large entropy and its disappearance under a magnetic field. Moreover, the energy scales characterizing these two sets of properties are very different: whereas the compressibility jump has an onset at a temperature of about 30 kelvin, the bandwidth of magnetic excitations is about 3 kelvin or smaller. The hybrid nature of the present correlated state and the large separation of energy scales have implications for the thermodynamic and transport properties of the correlated states in twisted bilayer graphene.

Suggested Citation

  • Asaf Rozen & Jeong Min Park & Uri Zondiner & Yuan Cao & Daniel Rodan-Legrain & Takashi Taniguchi & Kenji Watanabe & Yuval Oreg & Ady Stern & Erez Berg & Pablo Jarillo-Herrero & Shahal Ilani, 2021. "Entropic evidence for a Pomeranchuk effect in magic-angle graphene," Nature, Nature, vol. 592(7853), pages 214-219, April.
  • Handle: RePEc:nat:nature:v:592:y:2021:i:7853:d:10.1038_s41586-021-03319-3
    DOI: 10.1038/s41586-021-03319-3
    as

    Download full text from publisher

    File URL: https://www.nature.com/articles/s41586-021-03319-3
    File Function: Abstract
    Download Restriction: Access to the full text of the articles in this series is restricted.

    File URL: https://libkey.io/10.1038/s41586-021-03319-3?utm_source=ideas
    LibKey link: if access is restricted and if your library uses this service, LibKey will redirect you to where you can use your library subscription to access this item
    ---><---

    As the access to this document is restricted, you may want to search for a different version of it.

    Citations

    Citations are extracted by the CitEc Project, subscribe to its RSS feed for this item.
    as


    Cited by:

    1. Keshav Singh & Aaron Chew & Jonah Herzog-Arbeitman & B. Andrei Bernevig & Oskar Vafek, 2024. "Topological heavy fermions in magnetic field," Nature Communications, Nature, vol. 15(1), pages 1-12, December.
    2. Jiachen Yu & Benjamin A. Foutty & Yves H. Kwan & Mark E. Barber & Kenji Watanabe & Takashi Taniguchi & Zhi-Xun Shen & Siddharth A. Parameswaran & Benjamin E. Feldman, 2023. "Spin skyrmion gaps as signatures of strong-coupling insulators in magic-angle twisted bilayer graphene," Nature Communications, Nature, vol. 14(1), pages 1-7, December.
    3. Anushree Datta & M. J. Calderón & A. Camjayi & E. Bascones, 2023. "Heavy quasiparticles and cascades without symmetry breaking in twisted bilayer graphene," Nature Communications, Nature, vol. 14(1), pages 1-8, December.
    4. Le Liu & Shihao Zhang & Yanbang Chu & Cheng Shen & Yuan Huang & Yalong Yuan & Jinpeng Tian & Jian Tang & Yiru Ji & Rong Yang & Kenji Watanabe & Takashi Taniguchi & Dongxia Shi & Jianpeng Liu & Wei Yan, 2022. "Isospin competitions and valley polarized correlated insulators in twisted double bilayer graphene," Nature Communications, Nature, vol. 13(1), pages 1-7, December.
    5. Yiwen Zhang & Bo Xie & Yue Yang & Yueshen Wu & Xin Lu & Yuxiong Hu & Yifan Ding & Jiadian He & Peng Dong & Jinghui Wang & Xiang Zhou & Jianpeng Liu & Zhu-Jun Wang & Jun Li, 2024. "Extremely large magnetoresistance in twisted intertwined graphene spirals," Nature Communications, Nature, vol. 15(1), pages 1-9, December.
    6. Zheng Ren & Jianwei Huang & Hengxin Tan & Ananya Biswas & Aki Pulkkinen & Yichen Zhang & Yaofeng Xie & Ziqin Yue & Lei Chen & Fang Xie & Kevin Allen & Han Wu & Qirui Ren & Anil Rajapitamahuni & Asish , 2024. "Persistent flat band splitting and strong selective band renormalization in a kagome magnet thin film," Nature Communications, Nature, vol. 15(1), pages 1-9, December.
    7. Jesse C. Hoke & Yifan Li & Julian May-Mann & Kenji Watanabe & Takashi Taniguchi & Barry Bradlyn & Taylor L. Hughes & Benjamin E. Feldman, 2024. "Uncovering the spin ordering in magic-angle graphene via edge state equilibration," Nature Communications, Nature, vol. 15(1), pages 1-7, December.

    More about this item

    Statistics

    Access and download statistics

    Corrections

    All material on this site has been provided by the respective publishers and authors. You can help correct errors and omissions. When requesting a correction, please mention this item's handle: RePEc:nat:nature:v:592:y:2021:i:7853:d:10.1038_s41586-021-03319-3. See general information about how to correct material in RePEc.

    If you have authored this item and are not yet registered with RePEc, we encourage you to do it here. This allows to link your profile to this item. It also allows you to accept potential citations to this item that we are uncertain about.

    We have no bibliographic references for this item. You can help adding them by using this form .

    If you know of missing items citing this one, you can help us creating those links by adding the relevant references in the same way as above, for each refering item. If you are a registered author of this item, you may also want to check the "citations" tab in your RePEc Author Service profile, as there may be some citations waiting for confirmation.

    For technical questions regarding this item, or to correct its authors, title, abstract, bibliographic or download information, contact: Sonal Shukla or Springer Nature Abstracting and Indexing (email available below). General contact details of provider: http://www.nature.com .

    Please note that corrections may take a couple of weeks to filter through the various RePEc services.

    IDEAS is a RePEc service. RePEc uses bibliographic data supplied by the respective publishers.