Type II superconductivity in SrPd₂Ge₂

Previous investigations have shown that SrPd₂Ge₂, a compound isostructural with '122' iron pnictides but iron and pnictogen free, is a conventional superconductor with a single s-wave energy gap and a strongly three-dimensional electronic structure. In this work we reveal the Abrikosov vortex lattice formed in SrPd₂Ge₂ when exposed to magnetic field by means of scanning tunneling microscopy and spectroscopy. Moreover, by examining the differential conductance spectra across a vortex and estimating the upper and lower critical magnetic fields by tunneling spectroscopy and local magnetization measurements, we show that SrPd₂Ge₂ is a strong type II superconductor with κ ≫ 2^-1/2. Also, we compare the differential conductance spectra in various magnetic fields to the pair-breaking model of Maki and de Gennes for a dirty limit type II superconductor in the gapless region. This way we demonstrate that the type II superconductivity is induced by the sample being in the dirty limit, while in the clean limit it would be a type I superconductor with κ ≪ 2 ^-1/2, in concordance with our previous study (Kim et al (2012) Phys. Rev. B 85 014520).