Research ArticleCONDENSED MATTER PHYSICS

Tuning from failed superconductor to failed insulator with magnetic field

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Science Advances  14 Jun 2019:
Vol. 5, no. 6, eaav7686
DOI: 10.1126/sciadv.aav7686
  • Fig. 1 Phase diagram of La2–xBaxCuO4 with x = 0.125 in terms of sheet resistance and Hall coefficient.

    (A) Interpolated color contour plot of the sheet resistance Rs as a function of temperature and magnetic field. Black vertical marks indicate measurement temperatures. The regimes of 3D and 2D superconductivity (SC) with zero electrical resistance are labeled; the UQM phase occurs at fields above the dotted line. Characteristic fields H3D, H2D, and HUQM (defined in the text) are overplotted as solid, dashed, and dotted white lines, respectively (these results are for sample A1; for an analogous plot for sample A2, see fig. S1). (B) Hall coefficient as a function of temperature, with error bars obtained by averaging over the entire field range (0 to 35 T; see fig. S2) at each temperature. RH is effectively zero below 15 K, as expected for a superconductor, and it rises to the normal-state magnitude around ∼40 K. The upper dashed line indicates the magnitude of RH that would be expected in a one-band system with a nominal hole density of 0.125. Results are from sample A, as described in the text.

  • Fig. 2 Sheet resistance in zero magnetic field.

    Rs as a function of temperature for samples A (circles) and B (squares). Inset shows sample and standard four-probe measurement configuration. Sample A has voltage contacts on two edges, resulting in measurements labeled A1 and A2. The difference between samples A and B is consistent with a small c-axis contribution to the resistance of B due to a slight misorientation of the c axis.

  • Fig. 3 Sheet resistance as a function of magnetic field.

    Results at various temperatures for samples (A) A1, (B) A2, and (C) B. (D) to (F) show the same data plotted versus a scaled magnetic field, as discussed in the text. H2D corresponds to the field at which zero resistance is seen in A1, and a local maximum of RsRQ occurs in A2. Measurement temperatures are color coded, as indicated in (D). Rs was measured with an ac current of 31.6 μA (for plots of Rs versus T, see fig. S3).

  • Fig. 4 Current dependence of sheet resistance.

    Results for samples (A) A1 and (B) A2 at T = 5.0 K with various currents. A significant difference between measurements is observed only in the 2D SC regime. (C) Current dependence of sheet resistance at μ0H = 15 T ≈ μ0H2D at T = 0.98 K for samples A1 (diamonds) and A2 (circles), obtained by nonlinear dV/dI measurements with an ac current of ∼10 μA, in addition to the larger dc current (see Materials and Methods). (D) Variation of sheet resistance at HH2D as a function of temperature measured with dc current of 31.6 (filled symbols) and 200 μA (open symbols; further data are presented in fig. S4.)

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/6/eaav7686/DC1

    Estimation of c-axis misorientation for sample B.

    Fig. S1. Temperature-magnetic field phase diagram for A2.

    Fig. S2. Field dependence of Hall voltage at various temperatures.

    Fig. S3. Sheet resistance at constant magnetic field.

    Fig. S4. ac nonlinear resistivity at H2D for various temperatures.

    Fig. S5. Additional results for sample B.

    Fig. S6. Comparison between A1 and previous results for a similar sample.

  • Supplementary Materials

    This PDF file includes:

    • Estimation of c-axis misorientation for sample B.
    • Fig. S1. Temperature-magnetic field phase diagram for A2.
    • Fig. S2. Field dependence of Hall voltage at various temperatures.
    • Fig. S3. Sheet resistance at constant magnetic field.
    • Fig. S4. ac nonlinear resistivity at H2D for various temperatures.
    • Fig. S5. Additional results for sample B.
    • Fig. S6. Comparison between A1 and previous results for a similar sample.

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