Research ArticleMATERIALS SCIENCE

Bursting at the seams: Rippled monolayer bismuth on NbSe2

See allHide authors and affiliations

Science Advances  13 Apr 2018:
Vol. 4, no. 4, eaaq0330
DOI: 10.1126/sciadv.aaq0330
  • Fig. 1 Topography of the single monolayer of Bi grown on cleaved NbSe2.

    (A) (1000 Å)2 view showing ripples and domains. Ripples have a period of approximately five lattice constants. (B) Atomically resolved topographic image of 180 Å × 360 Å showing the triangular bismuth lattice, ripple structure, and Y junctions that form at the boundaries between the domains. Dark patches are missing atom defects. (C) Schematic illustration of the geometry constraints responsible for the Y junctions. Vbias = +100 mV, I = 200 pA.

  • Fig. 2 Atomic-resolution topographic image of SLB (yellow-red) on top of NbSe2 (blue).

    The step edge forms a ~150° obtuse angle. LDOS spectra within the dashed-line rectangle, showing a transition of the 2D NbSe2 CDW to a 1D pattern, are discussed in Fig. 6. “x” marks a defect that is seen again in Fig. 4. Inset diagram shows the two-step edges relative to the NbSe2 lattice. Vbias = +200 mV, I = 100 pA.

  • Fig. 3 Strip of data across the rippled region in Fig. 1B.

    (A) Topography. (B) Blue line is (averaged) topographic height variation along this strip. Red arrows show the (exaggerated) lateral atomic displacements with scale bar for arrow length.

  • Fig. 4 A displacement map of a section of the step in Fig. 2 from a vertical line at 50 to 200 Å.

    The defect at (180,50) in that figure is marked here with x. Length of arrows is proportional to atomic displacements relative to the Se layer. Arrows placed at every fourth atom for clarity. Note scale bar for arrow length.

  • Fig. 5 Spectroscopic scan in a (100 Å)2 region over a Bi to NbSe2 step.

    LDOS in the NbSe2 region (green) and the SLB region (peaks of the ripples in red and valleys in blue). The individual dots represent all spectra in the subregion, whereas the solid line represents the average. Subtracting the average peak and valley spectra around zero bias shows a peak (top view).

  • Fig. 6 Spectra taken near the 150° edge in the white rectangle of Fig. 2.

    (A) Each horizontal line represents the average of all spectra at a fixed distance (indicated by the y axis) from the step edge. Color scale denotes DOS versus energy (x axis). (B) Same data with color used to indicate distance from step edge. (C and D) Same as above, with the average spectrum of the entire region subtracted.

  • Fig. 7 Average NbSe2 and Bi layer spectra for a (100 Å)2 scan over a step edge.

    Theoretical spectrum uses the following parameters: ΔL0 = 1.24 meV, ΔS0 = 0 mV, ΓSL = 2.2 mV, ΓLSSL = 1/3, plus broadening by a modulation voltage of 300 μV. T = 370 mK. Spectra normalized by positive bias coherence peak.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/4/eaaq0330/DC1

    Bi films growth and topography

    Estimation of ripple wavelength

    Spectroscopy measurements

    Initial DFT calculations

    The superconducting gap

    fig. S1. Large-area topography.

    fig. S2. Single-layer triangular lattice Bi versus the bilayer Bi(110).

    fig. S3. Summary of DFT calculations.

    References (3135)

  • Supplementary Materials

    This PDF file includes:

    • Bi films growth and topography
    • Estimation of ripple wavelength
    • Spectroscopy measurements
    • Initial DFT calculations
    • The superconducting gap
    • fig. S1. Large-area topography.
    • fig. S2. Single-layer triangular lattice Bi versus the bilayer Bi(110).
    • fig. S3. Summary of DFT calculations.
    • References (31–35)

    Download PDF

    Files in this Data Supplement: