Research ArticlePHYSICS

Paramagnon drag in high thermoelectric figure of merit Li-doped MnTe

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Science Advances  13 Sep 2019:
Vol. 5, no. 9, eaat9461
DOI: 10.1126/sciadv.aat9461
  • Fig. 1 Transport properties of Li-doped MnTe.

    (A) Thermopower, (B) resistivity, (C) thermal conductivity, and (D) thermoelectric figure of merit ZT. The Li concentrations for all frames are shown in the inset of frame (B).

  • Fig. 2 Inelastic neutron scattering result.

    Inelastic neutron scattering data S(Q,E) obtained on MnTe doped with 3 at % Li at ARCS, SNS, in the AFM phase (A) and PM phase (B to D). Magnon bands visible in (A) are transformed into a paramagnon relaxation spectrum in the PM phase. The S(Q,E) obtained at HYSPEC in the AFM phase (E) reveals low-energy features of the magnon scattering and the pseudogap of ~0.6 meV at Q = 0.92 Å−1. The paramagnon full width at half maximum (FWHM) and lifetime (F) is obtained from fits to a slice in S(Q,E) (G). Data at 450 K were gathered on MnTe doped with 0.3, 1, 3, and 5 at % Li: No dependence of the FWHM (G) or lifetime (F) is observed with Li concentration.

  • Fig. 3 Hole concentration, mobility and relaxation time, and specific heat of Li-doped MnTe.

    (A) Carrier concentration of all samples from Hall measurements. (B) Specific heat analysis of 6% Li-doped sample. The black dots are measured specific heat; the dashed line at low temperature is electron specific heat. Assuming that the high-temperature plateau is the Dulong-Petit high-temperature limit, a Debye model is fitted to the data to calculate the phonon contribution. The difference between measured specific heat and Debye model plus electronic specific heat is then the magnetic contribution. (C) Sample mobility μ. (D) Electron relaxation time τe from mobility. The legend for all frames is shown in frame (C).

  • Fig. 4 Comparison between calculated thermopower and measured thermopower.

    The experimental temperature dependence of the thermopower of the samples doped with Li concentrations x = 0.01, 0.03, and 0.06 is compared to the calculated values. The low-temperature dashed line is the diffusion thermopower αd in the AFM regime; the full line is the sum of the calculated magnon-drag and diffusion thermopowers α = αd + αmd. In the PM regime, the lower dashed line is the calculated diffusion thermopower αd. The difference between this dashed line and the experimental data is attributed to paramagnon drag.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/9/eaat9461/DC1

    Fig. S1. Band structures of paramagnetic and antiferromagnetic hexagonal MnTe.

    Fig. S2. Comparison of the resistivity (left frame) and thermopower (right frame) of non-intentionally doped binary MnTe (black diamonds) and MnTe doped with 3% Li (red squares).

    Fig. S3. Phonon drag in Li-MnTe.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Band structures of paramagnetic and antiferromagnetic hexagonal MnTe.
    • Fig. S2. Comparison of the resistivity (left frame) and thermopower (right frame) of non-intentionally doped binary MnTe (black diamonds) and MnTe doped with 3% Li (red squares).
    • Fig. S3. Phonon drag in Li-MnTe.

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