Research ArticleCONDENSED MATTER PHYSICS

Slow dynamics of electrons at a metal–Mott insulator boundary in an organic system with disorder

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Science Advances  11 Aug 2017:
Vol. 3, no. 8, e1601594
DOI: 10.1126/sciadv.1601594
  • Fig. 1 Structure and transport properties of EtMe3Sb[Pd(dmit)2]2.

    (A) Side view of the layered structure of EtMe3Sb[Pd(dmit)2]2 (41). Mott-insulating Pd(dmit)2 layers are separated by closed-shell cation layers of EtMe3Sb. The cation layers have random orientations of the ethyl groups. (B) Temperature dependence of the in-plane resistivity of EtMe3Sb[Pd(dmit)2]2 under several pressures measured using the standard four-electrode method.

  • Fig. 2 Temperature dependence of the 13C nuclear spin-lattice relaxation rate (T1−1) of EtMe3Sb[Pd(dmit)2]2 under several pressures, reflecting the amplitude of the fluctuations of the internal magnetic field on a megahertz time scale.

    The dashed line shows a fit of the data at 15 kbar to the Korringa relation T1−1T.

  • Fig. 3 Profiles of the 13C nuclear spin-spin relaxation rate (T2−1) of EtMe3Sb[Pd(dmit)2]2 under several pressures.

    (A) Temperature dependence of T2−1 of EtMe3Sb[Pd(dmit)2]2 under several pressures. For comparison, data for EtMe3P[Pd(dmit)2]2 at ambient pressure are also plotted as open black circles. The left axis shows the observed raw value of the whole spin-spin relaxation rate. The value of T2l−1 (the right axis) is estimated by subtracting 640 s−1 from T2−1 (see Materials and Methods and the Supplementary Materials). (B) The two components of T2l−1 of EtMe3Sb[Pd(dmit)2]2. The amplitude of the blue component shows a peak at 10 to 30 K. The amplitude of the blue component at low temperatures (where both components exist) is estimated by extrapolating the trend at higher temperatures. The amplitude of the red component is enhanced at low temperatures. This enhancement is particularly prominent at 7 kbar, which is near the Mott boundary.

  • Fig. 4 Pressure-temperature phase diagram of the slow fluctuations in EtMe3Sb[Pd(dmit)2]2.

    (A) Schematic pressure-temperature phase diagram of the contour plot of the slow fluctuations in EtMe3Sb[Pd(dmit)2]2. The magnitudes of the charge and spin fluctuations are represented in red and blue, respectively. The intensities are determined by the amplitudes of the blue and red components of T2l−1 in Fig. 3B. (B) Pressure-temperature phase diagram of the contour plot of the conductivity (the inverse of the resistivity shown in Fig. 1B), for comparison. Note that the horizontal axes in the two panels stand for the value of the pressure applied at room temperature, and the actual pressure in the temperature region discussed in these phase diagrams is 1.5 to 2 kbar lower than the value on the horizontal axes.

  • Fig. 5 Schematic phase diagrams of Ising spin systems and Mott transition systems.

    (A) Field-temperature phase diagram of a clean Ising spin system. (B) Pressure-temperature phase diagram of a clean Mott transition system. (C) Field-temperature phase diagram of an Ising spin system with randomness. (D) Our proposed pressure-temperature phase diagram of a Mott transition system with randomness.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/8/e1601594/DC1

    section S1. Spin-spin relaxation

    section S2. Cation molecular motion

    fig. S1. 13C spin-spin relaxation curves as functions of 2τ (left) and (2τ)2 (right) for EtMe3Sb[Pd(dmit)2]2 and EtMe3P[Pd(dmit)2]2.

    fig. S2. Temperature dependence of the spin-lattice relaxation rate (T1−1) of the protons in the cation molecule of EtMe3Sb[Pd(dmit)2]2 at several pressures.

    Reference (42)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Spin-spin relaxation
    • section S2. Cation molecular motion
    • fig. S1. 13C spin-spin relaxation curves as functions of 2τ (left) and (2τ)2 (right) for EtMe3SbPd(dmit)22 and EtMe3PPd(dmit)22.
    • fig. S2. Temperature dependence of the spin-lattice relaxation rate (T1−1) of the protons in the cation molecule of EtMe3SbPd(dmit)22 at several pressures.
    • Reference (42)

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