Large oscillations of the magnetoresistance in nanopatterned high-temperature superconducting films

Journal name:
Nature Nanotechnology
Volume:
5,
Pages:
516–519
Year published:
DOI:
doi:10.1038/nnano.2010.111
Received
Accepted
Published online

Abstract

Measurements on nanoscale structures constructed from high-temperature superconductors are expected to shed light on the origin of superconductivity in these materials1, 2, 3, 4, 5, 6, 7. To date, loops made from these compounds have had sizes of the order of hundreds of nanometres8–11. Here, we report the results of measurements on loops of La1.84Sr0.16CuO4, a high-temperature superconductor that loses its resistance to electric currents when cooled below ~38 K, with dimensions down to tens of nanometres. We observe oscillations in the resistance of the loops as a function of the magnetic flux through the loops. The oscillations have a period of h/2e, and their amplitude is much larger than the amplitude of the resistance oscillations expected from the Little–Parks effect12, 13. Moreover, unlike Little–Parks oscillations, which are caused by periodic changes in the superconducting transition temperature, the oscillations we observe are caused by periodic changes in the interaction between thermally excited moving vortices and the oscillating persistent current induced in the loops. However, despite the enhanced amplitude of these oscillations, we have not detected oscillations with a period of h/e, as recently predicted for nanoscale loops of superconductors with d-wave symmetry1, 2, 3, 4, 5, 6, or with a period of h/4e, as predicted for superconductors that exhibit stripes7.

At a glance

Figures

  1. Patterned superconducting film.
    Figure 1: Patterned superconducting film.

    Main panel: scanning electron microscope (SEM) image of a La1.84Sr0.16CuO4 superconducting film covered with a patterned layer of poly(methyl methacrylate) (PMMA) resist (thin lines with bright edges). The left inset shows an SEM image of a part of the resulting superconducting network (150 × 150-nm2 loops separated by 500 × 500-nm2 loops) after the uncovered parts of the film were removed by ion milling. The right inset shows the measured (white circles) temperature dependence of the network (30 × 30 µm2) resistance in zero magnetic field near the superconducting transition; the current is 1 µA. In the patterned film the onset temperature for superconductivity is 30.2 K and the transition width is ~2 K (compared with 38 K and ~0.5 K for the as-grown film).

  2. Magnetoresistance oscillations.
    Figure 2: Magnetoresistance oscillations.

    Resistance of the La1.84Sr0.16CuO4 network shown in Fig. 1 as a function of applied magnetic field, measured at 28.4 K. The oscillations are superimposed on a parabolic-like background. The amplitude of the oscillations, ΔR, is well defined at low fields. Inset: ΔR as a function of temperature; the solid line is a theoretical fit based on equation (5). The dashed line is an upper limit for the amplitude of resistance oscillations calculated for the Little–Parks effect (right axis; note that the scale on this axis is expanded tenfold).

  3. Comparison of measured and calculated magnetoresitance oscillations.
    Figure 3: Comparison of measured and calculated magnetoresitance oscillations.

    a, Measured normalized resistance of the network shown in Fig. 1 as a function of the applied magnetic field and temperature. b, Normalized resistance calculated using equation (4) for wire width w = 25 nm, film thickness d = 26 nm, zero-temperature penetration depth λ0 = 750 nm and coherence length ξ0 = 2.4 nm. The calculation was made for circular loops of the same area as the square loops: that is, with an effective radius = a/π = 83.5 nm (a = 150 nm is the actual loop side length). The values for λ0 and ξ0 are obtained from the fit of equation (5) to the temperature dependence of the amplitude shown in the inset to Fig. 2. The colour changes from blue to green to orange to white as the resistance increases from zero to the normal-state value.

  4. Periodicity of the magnetoresistance oscillations.
    Figure 4: Periodicity of the magnetoresistance oscillations.

    a,b, Amplitude of the Fourier transform of the magnetoresistance oscillations versus inverse magnetic flux in the 150-nm loops at 28.5 K (a) and the 75-nm loops at 28 K (b). The h/2e periodicity is apparent, but the h/e periodicity is absent, and the h/4e periodicity appears as the second harmonic of the h/2e fundamental component.

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Affiliations

  1. Department of Physics, Institute of Superconductivity and Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel

    • Ilya Sochnikov,
    • Avner Shaulov &
    • Yosef Yeshurun
  2. Brookhaven National Laboratory, Upton, New York 11973-5000, USA

    • Gennady Logvenov &
    • Ivan Božović

Contributions

G.L and I.B. synthesized and characterized the superconducting films. I.S. designed and made the patterns, performed the magnetoresistance measurements and analysed the data. All authors contributed to the theoretical interpretation and were involved in the completion of the manuscript.

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The authors declare no competing financial interests.

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