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Evidence for dispersing 1D Majorana channels in an iron-based superconductor

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Science  03 Jan 2020:
Vol. 367, Issue 6473, pp. 104-108
DOI: 10.1126/science.aaw8419
  • Fig. 1 Band structure and superconductivity in FeSe0.45Te0.55.

    (A) Sketch of bulk Fermi surfaces of Fe(Se,Te) at momentum kz = 0. (B) Cartoon image showing superconductivity in the bulk and proximitized superconductivity in the topological surface state (31). (C) Topographic image in a 25- by 25-nm field of view (bias voltage VS = 40 mV, tunneling current It = 100 pA). (D) Scanning tunneling spectroscopy (STS) data taken along the line shown in (C) at 0.3 K [VS = 6 mV, It = 300 pA, modulation voltage (Vmod) = 58 μV]. The spectra are vertically offset for clarity.

  • Fig. 2 Statistical analysis of superconducting gaps.

    (A) 100- by 100-nm map depicting the distribution of superconducting gaps in FeSe0.45Te0.55. Blue, orange, and green colors indicate whether a single gap, two gaps, or three gaps were found at each pixel, respectively. The gap values at each pixel were obtained through a multipeak-finding algorithm (37). (B) STS spectra at 0.3 K obtained along the white line shown in (A), starting (top to bottom) with a two-gap region (orange), which transitions to a three-gap region (green) and ends in a single-gap region (blue). The spectra are vertically offset for clarity. (C) Histogram of the gap values in the one-, two-, and three-gap regions. The dark curves show Gaussian fits to the gap distribution, with mean gap values of 1.4, 1.9, and 2.4 meV.

  • Fig. 3 Signature of dispersing 1D Majorana modes at a DW.

    (A) 25- by 25-nm topographic image showing a DW (bright line) (VS = 4 mV, It = 250 pA). (B) 2D fast Fourier transform of (A), showing a splitting of the Bragg peaks, which indicates the presence of domains in this image. (Inset) Zoom-in near one of the Bragg peaks. (C) Height scans taken at different bias voltages along the yellow dashed line in (A). (D) Zoom-in of the DW. The white and red lines track the atomic lattice on both sides of the DW. A half-unit-cell shift can be observed between one side and the other. (E) Schematic of the half-unit-cell shift across the DW. The schematic also depicts how one might obtain a π-phase shift in the superconducting order parameter across such a DW. Superimposed on the lattice are red and green bars, which denote the parity of next-nearest-neighbor pairing (42, 43). As an example, tracking the atoms inside the dashed box, one can see that the parity shifts from red on the left of the DW to green on the right. This creates a π-phase shift in the superconducting order parameter. (F) Line-cut profiles of dI/dV spectra along the three blue lines in (A), which cross the DW (VS = 4 mV, It = 250 pA, Vmod = 58 μV). The spectra shapes obtained right on the DW [at position of dots in (A)] are highlighted with a dark blue color. For clarity, the spectra are vertically offset from each other by 0.06 (6 nS). (Inset) A direct comparison of the spectra taken on the DW (orange) and far away (black). All data were obtained at 0.3 K.

  • Fig. 4 Spatial distribution of the 1D Majorana mode at a DW with increasing energy.

    (A to F) dI/dV maps from 0 to 1.5 meV at 0.3 K. The maps are 25 by 25 nm in size, and spectra were obtained on a 130- by 130-pixel grid. DW states are present at all energies inside the gap up to 1 meV, when the states merge into the coherence peaks. However, the spatial extent of the states grows with increasing energy. (G) DOS profiles measured at different energies along the white line perpendicular to the DW.

Supplementary Materials

  • Evidence for dispersing 1D Majorana channels in an iron-based superconductor

    Zhenyu Wang, Jorge Olivares Rodriguez, Lin Jiao, Sean Howard, Martin Graham, G. D. Gu, Taylor L. Hughes, Dirk K. Morr, Vidya Madhavan

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods 
    • Supplementary Text
    • Figs. S1 to S13
    • Tables S1 and S2
    • References 

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