Tip-induced superconductivity enhancement in single-crystalline PdSb by point-contact spectroscopy

Abstract

We report our mechanical point-contact spectroscopy (MPCS) study on single-crystalline superconductor PdSb with Tc∼ 1.32 K and μ0Hc2(0)∼ 900 Oe, whose Tc changes very slightly against hydrostatic pressure below 2.5 GPa. For MPCS with a soft Au tip, the Andreev reflection signals suggest the same superconducting temperature Tc as in the pristine PdSb crystal and the conductance curves show a fully gapped behavior, yielding a superconducting gap value of Δ0= 0.23 meV with 2Δ0/kBTc∼ 4.25 in the strong-coupling regime. However, for MPCS with a hard W tip, an enhanced superconducting Tc can be observed with a concomitant increase in the superconducting gap Δ in a linear relation of 0.109 meV/kelvin, whereas 2Δ0/kBTc decreases from 4.25 to 3.5 in a negative correlation with Tc. From first-principles calculations, we observe a Lifshitz transition related to Pd-4dz2 orbitals under uniaxial pressure, which is absent under hydrostatic pressure. Such Lifshitz transition results in an enhanced density of states near the Fermi level n(EF), which is in line with the enhanced Tc. In addition, a soft phonon mode at H is hardened under uniaxial pressure, suggesting a reduced coupling strength in this case. Such local strain effect provides a natural explanation for our MPCS results on PdSb.

Source-reported materials — not catalogue approval

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