Magnetic Pair Breaking in Superconducting SrPd2Ge2 Investigated by Scanning Tunnelling Spectroscopy
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SrPd2Ge2 has been structurally identical with the 122-type iron pnictide compounds with iron completely replaced by Pd and pnictogen replaced by Ge yielding the superconducting transition below 3 K. Our previous works showed that in contrast to iron pnictides this system is electronically fully three-dimensional and revealed conventional superconductivity, even of type I. Here, by means of sub-Kelvin STM spectroscopy, we show that the dirty limit occurs in the sample driving it to type-II superconductivity. STM also proves that in magnetic field the sample undergoes the phase transition to the Abrikosov vortex-lattice state. The de Gennes–Maki theory of gapless superconductivity for dirty superconductors is successfully applied to model the tunnelling spectra of the superconducting density of states in magnetic field. We show that this theory is applicable in a wide range of magnetic fields starting from 60 % of the upper critical field H c2.
KeywordsSuperconducting pnictides SrPd2Ge2 Type I and type II superconductors Scanning tunnelling spectroscopy Vortex imaging Pair breaking
This work has been supported by the following projects: CFNT MVEP—the Centre of Excellence of the Slovak Academy of Sciences, FP7 MNT—ERA.Net II. ESO, the EU ERDF (European Union Regional Development Fund) Grant No. ITMS26220120005, VEGA 2/0148/10 and the project 2011-0028736 of the Ministry of Education, Science, and Technology of Korea. The liquid nitrogen for the experiment has been sponsored by the US Steel Kosice, s.r.o.
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