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Spin-gapped Mott insulator with the dimeric arrangement of twisted molecules Zn(tmdt)2

Rina Takagi, Hiro Gangi, Kazuya Miyagawa, Biao Zhou, Akiko Kobayashi, and Kazushi Kanoda
Phys. Rev. B 95, 224427 – Published 22 June 2017
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  • ACKNOWLEDGMENTS
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    Abstract

    C13 nuclear magnetic resonance measurements were performed for a single-component molecular material Zn(tmdt)2, in which tmdt's form an arrangement similar to the so-called κ-type molecular packing in quasi-two-dimensional Mott insulators and superconductors. A detailed analysis of the powder spectra uncovered local spin susceptibility in the tmdt π orbitals. The obtained shift and relaxation rate revealed singlet-triplet excitations of the π spins, indicating that Zn(tmdt)2 is a spin-gapped Mott insulator with exceptionally large electron correlations compared to conventional molecular Mott systems.

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    • Received 4 April 2017
    • Revised 25 May 2017

    DOI:https://doi.org/10.1103/PhysRevB.95.224427

    ©2017 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Magnetism
    1. Physical Systems
    Molecular solidsMott insulators
    1. Techniques
    Nuclear magnetic resonance
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Rina Takagi1,*, Hiro Gangi1, Kazuya Miyagawa1, Biao Zhou2, Akiko Kobayashi2, and Kazushi Kanoda1

    • 1Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
    • 2Department of Chemistry, College of Humanities and Sciences, Nihon University, Setagaya-ku, Tokyo 156-8550, Japan

    • *Present address: RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan.

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    Vol. 95, Iss. 22 — 1 June 2017

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    • Figure 1
      Figure 1

      (a) Molecular structure of Zn(tmdt)2. (b) Molecular arrangement in the Zn(tmdt)2 crystal. (c) End-on projection of the “κ-type” molecular arrangement in the tmdt layer. (d) Temperature dependence of two-probe resistivity for Zn(tmdt)2 measured on a single crystal of approximately 70 μm. The inset shows the Arrhenius plot and an activation energy Ea=91 meV was obtained from the data for 200–280 K (indicated by a red curve).

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    • Figure 2
      Figure 2

      (a) Temperature dependence of C13 NMR spectra for the polycrystalline Zn(tmdt)2. Solid (red) curves are fits described in the text. (b) Temperature dependence of the three principal values of the shift tensor δii (i=x, y, and z). The symbols correspond to those indicated in (a).

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    • Figure 3
      Figure 3

      (a) Temperature dependence of the isotropic part of NMR shift determined by the first moment of the spectra. The red line indicates the isotropic part of chemical shift σiso. (b) Temperature dependence of the anisotropic parts of NMR shifts; for example, the level of the blue line is equal to the anisotropic part of chemical shift σ1 and the deviation from that corresponds to −Kaniso. (c) Temperature dependence of spin susceptibility (with a Curie contribution subtracted) of the polycrystalline Zn(tmdt)2,which was fitted on the basis of the singlet-triplet excitation model (red curve). (d) Kiso–χ and (e) iKaniso–χ plots. Solid lines are the fits of the data. The curves in (a) and (b) are the χ curve [the red curve in (c)] multiplied by respective hyperfine coupling constants determined by the slopes in (d) and (e).

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    • Figure 4
      Figure 4

      (a) Nuclear spin-lattice relaxation rate T1−1 for Zn(tmdt)2. The symbols of squares and triangles represent the relaxation rates of the sample and a minor impurity phase (see text). (b) Temperature dependence of the stretched exponent β in the fitting of the nuclear relaxation (see text). (c) The activation plot of T1−1 for 200–300 K, where the relaxation rate of the sample is well separated from that of the minor impurity phase. The inset is the activation plot of (T1T)−1. (d) Spin model for the pπ electrons in the “κ-type” configuration of tmdt's in the two-dimensional layer.

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    • Figure 5
      Figure 5

      Scheme 1.

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    • Figure 6
      Figure 6

      Scheme 2.

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