Surface superconductivity on SrFe2As2 single crystals induced by ion implantation
Industrial Research Limited - P.O. Box 31310, Lower Hutt 5040, New Zealand
2 National Isotope Centre, GNS Science - P.O. Box 31312, Lower Hutt 5040, New Zealand
3 Institute of Materials Science and Graduate School of Pure & Applied Sciences, University of Tsukuba 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, Japan
Accepted: 26 March 2011
This study presents an unprecedented route in inducing superconductivity in SrFe2As2 single crystals by ion implantation. Na+ implantation into SrFe2As2 single crystals did not induce superconductivity nor did it shift the spin-density wave (SDW) anomaly at 205 K. In contrast, above a threshold of 2 at.% dosage, all the K+- and Ca2+-implanted crystals show a superconducting transition below 25 K in magnetisation and resistivity measurements. Due to the shallow implantation depth of the ions, the observed superconductivity is in principle confined to the surface or sub-surface level, and the normal state can be recovered by thermal annealing. This strongly suggests superconductivity in these samples is induced by surface or sub-surface crystallographic strain. The deduced anisotropy ratio of the upper critical field is above 3 in all the superconducting samples, and more important is the obtained c-axis coherence lengths are longer than the interlayer spacing in SrFe2As2 implying strong interlayer coupling in these superconductors.
PACS: 74.70.Xa – Pnictides and chalcogenides / 74.62.Dh – Effects of crystal defects, doping and substitution / 74.25.F- – Transport properties
© EPLA, 2011