Unusual Sensitivity of Superconductivity to Strain in Iron-Based 122 Superconductors

Abstract

Co-doped BaFe2As2 has been previously shown to have an unusually significant improvement of Tc (up to 2 K, or almost 10%) with annealing 1-2 weeks at 700 or 800 C, where such annealing conditions are insufficient to allow significant atomic diffusion. While confirming similar behavior in optimally Co-doped SrFe2As2 samples, the influence on Tc of strain induced by grinding to ~50 micron sized particles, followed by pressing the powder into a pellet using 10 kbar pressure, was found to increase the annealed transition width of 1.5 K by approximately a factor of ten. Also, the bulk discontinuity in the specific heat at Tc, deltaC, on the same pellet sample was completely suppressed by grinding. This evidence for a strong sensitivity of superconductivity to strain was used to optimize single crystal growth of Co-doped BaFe2As2. This strong dependence (both positive via annealing and negative via grinding) of superconductivity on strain in these two iron based 122 structure superconductors is compared to the unconventional heavy Fermion superconductor UPt3, where grinding is known to completely suppress superconductivity, and to recent reports of strong sensitivity of Tc to damage induced by electron-irradiation-induced point defects in other 122 structure iron-based superconductors, Ba(Fe0.76Ru0.24)2As2 and Ba1-xKxFe2As2. Both the electron irradiation and the introduction of strain by grinding are believed to only introduce non-magnetic defects, and argue for unconventional superconducting pairing.

References in corpus (6)

• High-temperature superconductivity in iron-based materials
• Superconductivity at 22 K in Co-doped BaFe2As2 Crystals
• Effects of electron irradiation on resistivity and London penetration depth of Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ ($x\le$ 0.34) iron - pnictide superconductor
• Specific Heat Discontinuity DeltaC vs Tc in Annealed Ba(Fe1-xCox)2As2
• Single-crystal growth of the ternary BaFe${}_2$As${}_2$ phase using the vertical Bridgman technique
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Cited by in corpus (1)

• Unconventional Superconductivity