Magnetic penetration depth in single crystals of SrPd2Ge2 superconductor

Abstract

The in-plane magnetic penetration depth λm(T) was measured in a single crystal of SrPd2Ge2 superconductor in a dilution refrigerator down to T=60 mK and in magnetic fields up to Hdc=1 T by using a tunnel diode resonator. The London penetration depth λ saturates exponentially approaching T→0 indicating fully gapped superconductivity. The thermodynamic Rutgers formula was used to estimate λ(0)=426±60 nm which was used to calculate the superfluid density, ρs(T)=λ2(0)/λ2(T). Analysis of ρs(T) in the full temperature range shows that it is best described by a single-gap behavior, perhaps with somewhat stronger coupling. In a magnetic field, the measured penetration depth is given by the Campbell penetration depth which was used to calculate the theoretical critical current density jc. For H≤0.45 T, the strongest pinning is achieved not at the lowest, but at some intermediate temperature, probably due to matching effect between temperature-dependent coherence length and relevant pinning length scale. Finally, we find compelling evidence for surface superconductivity. Combining all measurements, the entire H-T phase diagram of SrPd2Ge2 is constructed with an estimated Hc2(0)=0.4817 T.

Source-reported materials — not catalogue approval

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