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Dominant nonlocal superconducting proximity effect due to electron-electron interaction in a ballistic double nanowire

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Science Advances  04 Oct 2019:
Vol. 5, no. 10, eaaw2194
DOI: 10.1126/sciadv.aaw2194
  • Fig. 1 Device structure and normal state conductance.

    (A) SEM image of the device. Two Al electrodes (blue) spaced by approximately 20 nm are placed on an InAs DNW. Two top gate electrodes (orange) spaced by approximately 80 nm are contacted to the DNW. Scale bar, 400 nm. (B) Schematic image of the device. NW1 and NW2 are mainly gated by electrode g1 with voltage Vg1 and electrode g2 with voltage Vg2, respectively. (C) Differential conductance G in units of e2/h as a function of Vg1 and Vg2 measured for magnetic field B = 250 mT and 50 mK. The blue (red) solid line follows the NW1 (NW2) pinch-off points. The dashed lines parallel to the solid lines indicate transitions between the respective NW plateaus [see (D)]. (D) G against Vg1 (blue) was measured by setting Vg2 between −5.0 and −8.0 V, where NW2 is pinched off, and G against Vg2 (red) was measured by setting Vg1 between −17.0 and −20.0 V, where NW1 is pinched off. All conductance curves show plateau-like features at 2, 4, and 6 e2/h, as shown by the bold curves. (E) G plotted along the purple solid line in (C), where both NWs are equally populated. The conductance shows plateaus of 4 and 8 e2/h when both NWs have two and four propagating channels, respectively.

  • Fig. 2 Supercurrent due to LPT into each NW.

    (A) Typical differential resistance R against bias current I at B = 0 T measured in the conductance plateau regions of (2,0), (4,0), and (6,0), respectively, as shown in Fig. 1D. The supercurrent flows in the Josephson junction in the region of R ≃ 0 Ω. Isw is evaluated from the peak position. (B) Isw against G derived from measurement results shown in (A). The bars indicate variations of Isw and G in the measurement performed at various points of the respective plateaus. Isw monotonically depends on G. (C and D) Identical plots to (A) and (B), respectively, but for the conductance plateau regions of (0,2), (0,4), and (0,6).

  • Fig. 3 Supercurrents in various conductance plateau regions.

    (A) Differential resistance R against I in the conductance plateau regions of (2,0), (0,2), and (2,2). Isw in the (2,2) region is much larger than the sum of the Isw values in the (2,0) and (0,2) regions. (B) R against I in the conductance plateau regions of (4,0), (0,4), and (4,4). The sum of the Isw value in the (4,4) region is much larger than the sum of the Isw values in the (4,0) and (0,4) regions. (C) Isw(m, n) against G(m, n) in the conductance plateau regions (m, n) = (2,2), (2,4), (4,2), (2,6), (6,2), and (4,4), respectively, and the sum of Isw(m, 0) and Isw(0, n) against the sum of G(0, n) and G(m, 0) in the conductance plateau regions (0, n) = (0,2) and (0,4) and (m, 0) = (2,0) and (4,0). The bars indicate variations of Isw and G in the measurement performed at various points of the respective plateaus. Isw(m, n) is significantly larger than Isw(n, 0) + Isw(0, m) because of the CPS contribution to the DNW.

  • Fig. 4 CPS efficiency and gap energies of the interwire and intrawire superconductivity.

    (A) Schematic table of Isw and CPS efficiency η obtained for various m and n values. Isw enhancement due to CPS is observed for all conductance plateaus in the DNW regions. The CPS η is significantly larger than 50% in the (2,2) region. (B) Estimated superconducting gap energies and the ratio of the interwire and intrawire superconductivity ξ in the respective (m, n) regions. ξ is larger than unity in the (2,2) and (2,4) regions.

  • Fig. 5 Magnetic field dependence of CPS and LPT components.

    Isw(2,2) and Isw(2,0) + Isw(0,2) measured at various magnetic fields of B = 0 to 180 mT. Isw(2,2) arises from both LPT into separate NWs and CPS into both NWs. The purple-shaded region corresponds to the Isw enhancement due to CPS. The CPS component gradually decreases and vanishes at B = 80 mT, whereas the LPT component is unchanged up to B = 80 mT and then decreases down to Isw = 0 nA at B = 160 mT.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/10/eaaw2194/DC1

    Fig. S1. Atomic force microscopy images of the nanowires before deposition of Al contact electrodes.

    Fig. S2. SEM image of a device similar to the one measured but before depositing the top gate electrodes.

    Fig. S3. Differential conductance (G) properties of the Al-InAs DNW-Al junction device.

    Fig. S4. Differential conductance G against Vsd measured at B = 0 T for a bias point on the respective plateau of (m, n).

    Fig. S5. Gate bias points set for supercurrent measurement at B = 0 T indicated on the surface plot of G against Vg1 and Vg2 at B = 250 mT.

    Fig. S6. Magnetic field dependence of Isw(m, n) and Isw(m, 0) + Isw(0, n) measured at various quantized conductance plateaus with m and n.

    Fig. S7. Isw(m, 0) + Isw(0, n) against G(m, 0) + G(0, n) measured at B = 80 mT and B = 120 mT.

    Fig. S8. Isw(2,2) as a function of temperature.

    Note S1. Details of fabrication process for the DNW Josephson junctions

    Note S2. Magnetic field dependence of the superconducting gap

    Note S3. Multiple Andreev reflection and quantized conductance outside the superconducting gap

    Note S4. Measurement points for supercurrent

    Note S5. Magnetic field dependence of CPS and LPT

    Note S6. Another possible mechanism for the Isw enhancement

    Note S7. Joule heating

    References (4350)

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Atomic force microscopy images of the nanowires before deposition of Al contact electrodes.
    • Fig. S2. SEM image of a device similar to the one measured but before depositing the top gate electrodes.
    • Fig. S3. Differential conductance (G) properties of the Al-InAs DNW-Al junction device.
    • Fig. S4. Differential conductance G against Vsd measured at B = 0 T for a bias point on the respective plateau of (m, n).
    • Fig. S5. Gate bias points set for supercurrent measurement at B = 0 T indicated on the surface plot of G against Vg1 and Vg2 at B = 250 mT.
    • Fig. S6. Magnetic field dependence of Isw(m, n) and Isw(m, 0) + Isw(0, n) measured at various quantized conductance plateaus with m and n.
    • Fig. S7. Isw(m, 0) + Isw(0, n) against G(m, 0) + G(0, n) measured at B = 80 mT and B = 120 mT.
    • Fig. S8. Isw(2,2) as a function of temperature.
    • Note S1. Details of fabrication process for the DNW Josephson junctions
    • Note S2. Magnetic field dependence of the superconducting gap
    • Note S3. Multiple Andreev reflection and quantized conductance outside the superconducting gap
    • Note S4. Measurement points for supercurrent
    • Note S5. Magnetic field dependence of CPS and LPT
    • Note S6. Another possible mechanism for the Isw enhancement
    • Note S7. Joule heating
    • References (4350)

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