Research ArticleCONDENSED MATTER PHYSICS

Unconventional scaling of the superfluid density with the critical temperature in transition metal dichalcogenides

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Science Advances  29 Nov 2019:
Vol. 5, no. 11, eaav8465
DOI: 10.1126/sciadv.aav8465

Figures

  • Fig. 1 Schematic phase diagram and TF μSR time spectra for NbSe2.

    (A) Crystal structure of 2H-NbSe2. (B) Pressure dependence of Tc and the CDW temperature TCDW (5). The red arrows mark the pressures at which the T dependence of the penetration depth was measured. The TF spectra, above and below Tc at pressures of (C) p = 0 GPa and (D) p = 2.2 GPa, are shown. The solid lines in (C) and (D) represent fits to the data by means of Eq. 4. The dashed lines are guides to the eyes.

  • Fig. 2 Superconducting muon spin depolarization rate σSC for NbSe2.

    Temperature dependence of σSC(T) measured in 4H-NbSe2 at ambient pressure and in 2H-NbSe2 at various hydrostatic pressures in an applied magnetic field of μ0H = 70 mT.

  • Fig. 3 Pressure evolution of various quantities.

    (A) The temperature dependence of λ−2 measured at ambient pressure for 4H-NbSe2 and at various applied hydrostatic pressures for 2H-NbSe2. The solid lines correspond to a two-gap (s + s)-wave model, and the dashed line represents a fit using a single-gap s-wave model. (B) Pressure dependence of Tc and the zero-temperature value of λ−2(0). (C) Pressure dependence of the zero-temperature values of the small superconducting gap Δ1 and the large superconducting gap Δ2.

  • Fig. 4 Superfluid density versus Tc.

    (A) Logarithmic plot of Tc against the λ−2(0) obtained from our μSR experiments in 2H-NbSe2, 4H-NbSe2, and MoTe2. The dashed red line represents the linear fit to the MoTe2 data. Uemura relation for hole- and electron-doped cuprates are shown as solid (31, 5355) and dashed lines (57), respectively. The points for various conventional BCS superconductors are also shown. (B) Linear plot of Tc against the λ−2(0). Inset shows the Tc against the λ−2(0) as a function of pressure for optimally doped cuprate superconductor La2−xBaxCuO4 (73).

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