The Pomeranchuk Effect in Magic Angle Graphene Revealed by Electronic Entropy Measurements

ORAL  · Invited

Abstract

In the 1950's, Pomeranchuk predicted that, counterintuitively, liquid 3He may solidify upon heating, due to a high excess spin entropy in the solid phase. In this talk, I will review our electronic entropy and compressibility measurements, which demonstrate an analogous electronic effect in magic angle twisted bilayer graphene. Our experiments reveal a giant magnetic entropy (~1kB per moiré site) near a filling of one electron per moiré site. This entropy drives a Pomeranchuk-like transition from a rather convention metal to a correlated state with nearly-free magnetic moments. However, while in 3He it is easy to understand why the spins of localized atoms in the solid are practically free, it is very surprising to observe nearly-free moments in a metallic, compressible state in magic angle graphene. The nature of this newly observed correlated metallic state is thus still highly puzzling.

1. Rozen, A. et al. Entropic evidence for a Pomeranchuk effect in magic angle graphene. Nature 592, 214-219 (2021).

*We acknowlegde the Leona M. and Harry B. Helmsley Charitable Trust grant, ISF grants (numbers 712539 and 13335/16), the Deloro award, the Sagol Weizmann-MIT Bridge programme, the ERC-Cog (See-1D-Qmatter, grant number 647413), the ISF Research Grants in Quantum Technologies and Science Program (grant numbers 994/19 and 2074/19), the DFG (CRC/ Transregio 183), the ERC-Cog (HQMAT, grant number 817799), EU Horizon 2020 (LEGOTOP 788715), the Binational Science Foundation (NSF/BMR-BSF grant number 2018643), the US Department of Energy (DOE), Office of Basic Energy Sciences (BES), Division of Materials Sciences and Engineering under award DE-SC0001819 (J.M.P.), the National Science Foundation (grant number DMR-1809802), the STC Center for Integrated Quantum Materials (NSF grant number DMR-1231319) (Y.C.), the Gordon and Betty Moore Foundation's EPiQS Initiative through grant GBMF9643, Fundación Ramón Areces, the US DOE Office of Science, BES (DE-SC0019300), the Elemental Strategy Initiative conducted by the MEXT, Japan (grant number JPMXP0112101001), JSPS KAKENHI grant number JP20H00354, the CREST (JPMJCR15F3), JST, the Materials Research Science and Engineering Center Shared Experimental Facilities supported by the NSF (DMR-0819762) and Harvard's CNS supported by the NSF (grant number ECS-0335765).

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Publication: 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 and Shahal Ilani, Entropic evidence for a Pomeranchuk effect in magic angle graphene, Nature 592, 214-219 (2021).

Presenters

  • shahal ilani

    • Weizmann Institute of Science

Authors

  • shahal ilani

    • Weizmann Institute of Science