Type II superconductivity in SrPd₂Ge₂

Abstract

Abstract.Previous investigations have shown that SrPd 2 Ge 2 , 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 SrPd 2 Ge 2 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 SrPd 2 Ge 2 is a strong type II superconductor with » 2 -½ . Also, we compare the differential conductance spectra in various magnetic fields to the pair breaking model of Maki -de Gennes for 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  « 2 -½ , in concordance with our previous study (T. Kim et al., Phys. Rev. B 85, (2012)).

Magnetic field dependence of the density of states in the multiband superconductorβ−Bi2Pd

“…The latter is calculated by summing over relevant neighbors (r i ) using σ 0 (r) = i 1 − tanh((r i − r)/ξ ) (dark dashed line) with ξ = 23 nm. This approximation agrees with microscopic calculations showing that the intervortex density of states for single band superconductors in the dirty limit is practically negligible for fields below about half H c2 [47][48][49]. The magnetic field increase of the intervortex density of states is pronounced, as shown by the blue points in Fig.…”

Single-gap superconductivity inβ−Bi2Pd

“…The scanning tunneling spectroscopy experiments were performed by means of a homemade scanning tunneling microscope (STM) head inserted in a commercial Janis SSV cryomagnetic system with a 3 He refrigerator and controlled by the Nanotec's Dulcinea SPM electronics [18]. In order to obtain a clean sample surface, the sample was cleaved shortly before inserting into the refrigerator, and the system was pumped to a high vacuum to minimize the contamination of the sample surface.…”

Magnetic penetration depth in single crystals of SrPd2Ge2superconductor

“…4 The London penetration depth and coherence length are reported to be λ(0) = 566 nm and ξ(0) = 21 nm 5 and λ(0) = 345 ± 30 nm ξ(0) = 25.6± 0.5 nm. 6 These values give the Ginzburg -Landau parameter of κ = 27 5 and κ = 13.5 6 , which makes SrPd 2 Ge 2 a strong type-II superconductor. Furthermore, thermodynamic 2 and tunneling spectroscopy measurements are consistent with a slightly strong -coupling s-wave Bardeen-Cooper-Schrieffer (BCS) superconductor with the zerotemperature value of the superconducting gap of ∆ 0 ≈ 2k B T c 5,6 , -not far from the weak coupling value of 1.76.…”