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Nearly Room-Temperature Ferromagnetism in a Pressure-Induced Correlated Metallic State of the van der Waals Insulator CrGeTe3

Dilip Bhoi, Jun Gouchi, Naoka Hiraoka, Yufeng Zhang, Norio Ogita, Takumi Hasegawa, Kentaro Kitagawa, Hidenori Takagi, Kee Hoon Kim, and Yoshiya Uwatoko
Phys. Rev. Lett. 127, 217203 – Published 17 November 2021
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    Abstract

    A complex interplay of different energy scales involving Coulomb repulsion, spin-orbit coupling, and Hund’s coupling energy in 2D van der Waals (vdW) material produces a novel emerging physical state. For instance, ferromagnetism in vdW charge transfer insulator CrGeTe3 provides a promising platform to simultaneously manipulate the magnetic and electrical properties for potential device implementation using few nanometers thick materials. Here, we show a continuous tuning of magnetic and electrical properties of a CrGeTe3 single crystal using pressure. With application of pressure, CrGeTe3 transforms from a ferromagnetic insulator with Curie temperature TC∼66  K at ambient condition to a correlated 2D Fermi metal with TC exceeding ∼250  K. Notably, absence of an accompanying structural distortion across the insulator-metal transition (IMT) suggests that the pressure induced modification of electronic ground states is driven by electronic correlation furnishing a rare example of bandwidth-controlled IMT in a vdW material.

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    • Received 12 July 2021
    • Accepted 8 October 2021

    DOI:https://doi.org/10.1103/PhysRevLett.127.217203

    © 2021 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Electrical conductivityExchange interactionFerromagnetismHopping transportMagnetic susceptibilitySecond order phase transitionsSpin-orbit coupling
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Dilip Bhoi1,*, Jun Gouchi1, Naoka Hiraoka2, Yufeng Zhang1,3, Norio Ogita4, Takumi Hasegawa4, Kentaro Kitagawa2, Hidenori Takagi2,5,6, Kee Hoon Kim7,8, and Yoshiya Uwatoko1

    • 1The Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
    • 2Department of Physics, Graduate School of Sciences, University of Tokyo, Tokyo 113-0033, Japan
    • 3School of Physics, Southeast University, Nanjing 211189, China
    • 4Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8521, Japan
    • 5Institute for Functional Matter and Quantum Technologies, University of Stuttgart, 70569 Stuttgart, Germany
    • 6Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart, Germany
    • 7Department of Physics and Astronomy, CeNSCMR, Seoul National University, Seoul 151-747, Republic of Korea
    • 8Institute of Applied Physics, Seoul National University, Seoul 151-747, Republic of Korea

    • *dilipkbhoi@issp.u-tokyo.ac.jp

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    Issue

    Vol. 127, Iss. 21 — 19 November 2021

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    Images

    • Figure 1
      Figure 1

      (a) A single layer of CrGeTe3. In CrX3, the place of Ge-Ge dimers remains vacant. (b) Crystalline electric field splitting of Cr 3d orbitals into t2g manifolds and eg manifolds. Δ is the energy difference between t2g levels and eg levels. JHTe is the Hund’s coupling energy at the Te site. (c) Schematic picture of FM superexchange interaction between Cr eg orbitals via two Te p orbitals. tpd(tp′d′) is the virtual hopping between eg(eg′) and p(p′) orbitals. θ is the geometrical Cr─Te─Cr bond angle. (d) In plane resistivity, ρab. (e) Zero field-cooled (ZFC) magnetic susceptibility χ at H=0.1  T applied along c axis. Inset: temperature derivative of dχ/dT.

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    • Figure 2
      Figure 2

      (a) Top: ZFC dc susceptibility of CrGeTe3 crystal S1 up to 1.73 GPa. Bottom: temperature dependence of dχ/dT. Field-cooled (FC) susceptibility for crystal (b) S2 and (c) S3. Field dependence of magnetization, M(H), for (d) S2 and (e) S3 at T=1.8  K under different pressure. Red arrows represent the direction of increasing pressure. (f) Curie-Weiss plot, 1/χ vs T, of crystal S3 at some selected pressure.

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    • Figure 3
      Figure 3

      (a) In plane resistivity ρab of CrGeTe3 at several pressures ranging from 0 to 11.0 GPa. The magenta dotted line represents an estimate of the Mott-Ioffe-Regel limit of resistivity, ρM2D. (b) ρab in logarithmic temperature scale. Red solid lines are −log(T) fit to ρab. (c) Δρab=(ρab−ρ0) vs T2 for P≥7.5  GPa, where ρ0 is the residual resistivity. The black line is a linear fit to Δρab at 7.5 GPa confirming a Fermi liquid state below TFL. (d) Out of plane resistivity ρc and (e) resistivity anisotropy ρc/ρab at some selected pressure.

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    • Figure 4
      Figure 4

      (a) Pressure-temperature phase diagram of CrGeTe3. Color scale represents the magnitude of ρab. θCW and TCχ are estimated from magnetic susceptibility. TCρ and TFL are determined from ρab. (b) Pressure dependence of effective moment, μeff, and saturation magnetic moment MS (at T=1.8  K). (c) and (d) are pressure dependence of ρc and ρab at T=10  K, respectively.

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