Isospin Pomeranchuk effect and finite temperature resistance minimum in rhombohedral graphene

ORAL

Abstract



Magnetism typically arises from the effect of exchange interactions on highly localized fermionic wave functions in f- and d-atomic orbitals. In rhombohedral graphene multilayers, in contrast, magnetism---manifesting as spontaneous polarization into one or more spin and valley flavors originates from fully itinerant electrons near a Van Hove singularity. Here, we study the electronic compressibility, proximal exciton sensing, and electronic transport measurements of Bernal Bilayer Graphene (BBG) and Rhombohedral Trilayer Graphene (RTG) devices as a prototypical example for itinerant magnetism. While magnetic ordering - observed most clearly via the onset of the anomalous Hall effect in valley polarized phases—occurs only below 2-3K, we find a fluctuation regime persisting to temperature more than one order of magnitude higher with an associated large excess entropy of ~0.8kB/charge carrier. As a consequence, increasing temperature can favor the formation of a fluctuating ordered phase, analogous to the Pomeranchuk effect in 3He. In temperature dependent transport measurements, we observe a decreasing resistance with increasing temperature throughout the fluctuation regime, a highly unusual behavior for metals. The negative temperature coefficients lead to a minimum of R(T) within the fluctuation phases of around 10-20K. We connect the negative dR/dT to the fluctuation regime and discuss possible mechanisms.

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Presenters

  • Ludwig Holleis

    University of California Santa Barbara, University of California, Santa Barbara

Authors

  • Ludwig Holleis

    University of California Santa Barbara, University of California, Santa Barbara

  • Tian Xie

    University of California, Santa Barbara

  • Haoxin Zhou

    University of California, Berkeley and Lawrence Berkeley National Laboratory, University of California, Berkeley

  • Siyuan Xu

    UCSB, University of California, Santa Barbara, University of California Santa Barbara

  • Caitlin L Patterson

    University of California, Santa Barbara

  • Archisman Panigrahi

    Massachusetts Institute of Technology

  • Takashi Taniguchi

    National Institute for Materials Science, International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan, International Center for Materials Nanoarchitectonics, National Institute of Material Science, Tsukuba, Japan, Advanced Materials Laboratory, National Institute for Materials Science

  • Kenji Watanabe

    National Institute for Materials Science, NIMS, Research Center for Functional Materials, National Institute for Materials Science, Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan, Research Center for Functional Materials, National Institute of Material Science, Tsukuba, Japan, National Institute of Materials Science, Advanced Materials Laboratory, National Institute for Materials Science

  • Leonid Levitov

    Massachusetts Institute of Technology

  • Chenhao Jin

    University of California, Santa Barbara, Cornell University, University of California at Santa Barbara

  • Erez Berg

    Weizmann Institute of Science

  • Andrea F Young

    University of California, Santa Barbara, University of California Santa Barbara, University of California at Santa Barbara