Research ArticlePHYSICS

Emergence of Kondo lattice behavior in a van der Waals itinerant ferromagnet, Fe3GeTe2

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Science Advances  12 Jan 2018:
Vol. 4, no. 1, eaao6791
DOI: 10.1126/sciadv.aao6791
  • Fig. 1 Crystal structure of FGT.

    (A) Side and (B) top views of the crystal structure of FGT. Inequivalent Fe sites are labeled as I and II, respectively. The most possible cleaving plane parallel to the (001) surface is shown in green. (C) The bulk and projected Brillouin zones of FGT. (D) XRD pattern for the as-grown facet of FGT single crystals, with (001) diffraction peaks observed exclusively. The insert is an image of FGT compound revealed by scanning electron microscopy. a.u., arbitrary units. (E) STM step and (G) atomic resolution images (0.3 V, 100 pA) on the cleaved (001) surface of FGT. (F) The step height and (H) nearest-neighbor atomic distance are measured from the profiles of the line sections in (E) and (G), respectively.

  • Fig. 2 Valence band structures of FGT.

    (A and B) Photoemission intensity map at EF integrated over a window (EF, − 10 and +10 meV) with p-polarized light and the corresponding FS sheets by tracking Fermi crossings. (C and D) Photoemission intensity plot and its angle-integrated photoemission spectroscopy (AIPES) with p-polarized light along cut 1 in (B). (E and F) Photoemission intensity plot and its AIPES with He I light along cut 2 in (B).

  • Fig. 3 Spectral weight transfer in the FM state.

    (A) Photoemission intensity map at EF integrated over a window (EF, −10 and +10 meV) around the K point with He I light at 80 K. (B) Temperature dependence of the band structure along cut 3 in (A), warming up from 80 to 300 K and then cooling back to 80 K. The nearly unchanged data quality excludes the possibility of surface aging as being responsible for the observed effect. (C) Temperature dependence of the AIPES divided by the Fermi-Dirac function and normalized at a 750-meV BE. The integrated range is marked by the solid rectangle in (B7). (D) The AIPES data at 80 and 300 K in (C). The curve in the lower panel corresponds to the AIPES spectrum at 80 K subtracted by that measured at 300 K. (E) Temperature dependences of the relative areas of the peak, dip, and hump in (D). The relative areas are normalized by the dip area at 80 K. (F) Curvature intensity maps around the K point at 80 and 260 K, respectively. The white dashed ellipses are visual guides. (G) Extracted momentum distribution curves (MDCs) dispersion of band γ. The solid and dotted lines represent the calculated and experimental results, respectively. The red lines represent the dispersions in the paramagnetic (PM) state, whereas other lines represent those in the FM state. (H) The temperature dependences of MDC peak widths at EF (black squares) and MDC peak position shifts (red squares) of band γ. The peak position shifts are defined as kFk(150 meV), where kF is the Fermi vector, and k(150 meV) is the MDC peak position at a 150-meV BE.

  • Fig. 4 Emergence of the Fano resonance peak at low temperature.

    (A and B) dI/dV maps (200 pA) on the same field at 6 K with bias voltages of −50 and +25 mV, respectively. (C) Spatial-resolved low-energy dI/dV spectra measured at the eight locations marked in (A) and (B). Two peaks located at −50 meV (A) and +25 meV (B) are marked with dashed lines. (D) Spatially averaged dI/dV spectra taken at different temperatures. The two peaks are marked with the red dashed line and green shadow, respectively. (E) Theoretical simulation (red curve) of the experimental dI/dV spectrum (black dots) at 6 K. The simulated Fano feature (green curve) is subtracted from the raw data, and the remaining peak is fitted by a Lorentzian term (purple curve). The Fano and Lorentzian terms are shifted for clarity. (F) Temperature dependence of the Fano resonance width extracted from the fitting in (E). The red line represents the temperature dependence of the width for a single Kondo impurity.

  • Fig. 5 Coherent-incoherent crossover in the FM state.

    (A and B) Temperature dependence of resistivity and magnetic susceptibility for FGT. The dashed lines in (A) are two tentative T linear trends to extract the value of T*. The bold green and orange lines mark the crossover and PM-FM transition, respectively. (C) Spin-up and (D) Spin-down band structures of Te-terminated FGT. The black line is the experimentally observed flat band η in Figs. 2 and 3. The bold green lines in the lower panel in (D) represent the hybridization between strongly dispersive bands and weakly dispersive bands near EF.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/1/eaao6791/DC1

    fig. S1. Hysteresis loop for H parallel to the c axis at 2 K.

    fig. S2. Spectral weight transfer at other momentum locations.

    fig. S3. Enlarged Fermi surface volume in the FM state.

    fig. S4. Spatial-resolved low-energy dI/dV spectra at different temperatures.

    fig. S5. Band structures of Te-terminated FGT in the PM state.

    fig. S6. The positive correlation between ferromagnetism and Kondo lattice behavior.

    References (5365)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Hysteresis loop for H parallel to the c axis at 2 K.
    • fig. S2. Spectral weight transfer at other momentum locations.
    • fig. S3. Enlarged Fermi surface volume in the FM state.
    • fig. S4. Spatial-resolved low-energy dI/dV spectra at different temperatures.
    • fig. S5. Band structures of Te-terminated FGT in the PM state.
    • fig. S6. The positive correlation between ferromagnetism and Kondo lattice behavior.
    • References (53–65)

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