Abstract
The low-temperature scanning tunneling microscope and spectroscopy (STM/STS) are used to visualize superconducting states in the cleaved single crystal of 9% praseodymium-doped CaFe2As2 (Pr-Ca122) with Tc ≈ 30 K. The spectroscopy shows strong spatial variations in the density of states (DOS), and the superconducting map constructed from spectroscopy discloses a localized superconducting phase, as small as a single unit cell. The comparison of the spectra taken at 4.2 K and 22 K (below vs. close to the bulk superconducting transition temperature) from the exact same area confirms the superconducting behavior. Nanoscale superconducting states have been found near Pr dopants, which can be identified using dI/dV conductance maps at +300 mV. There is no correlation of the local superconductivity to the surface reconstruction domain and surface defects, which reflects its intrinsic bulk behavior. We, therefore, suggest that the local strain of Pr dopants is competing with defects induced local magnetic moments; this competition is responsible for the local superconducting states observed in this Fe-based filamentary superconductor.
Highlights
IntroductionDiscovery of the high-Tc of Fe-based superconductors has attracted much attention recently
Accepted: 14 April 2021Discovery of the high-Tc of Fe-based superconductors has attracted much attention recently
The spectroscopy shows strong spatial variations of density of states, and a superconducting map constructed from spectroscopy discloses a localized superconducting phase, as small as a single unit cell
Summary
Discovery of the high-Tc of Fe-based superconductors has attracted much attention recently. 122-type iron-based superconductivity is of particular interest due to its relatively simple structure and the easy growth of large single crystals [1]. The parent compound of the 122 family exhibits antiferromagnetic order at low temperature, and the superconductivity typically emerges through chemically doping. The mechanism of doping-induced superconductivity in 122 superconductors is still controversial. The superconducting doped samples are electronically inhomogeneous, even on a nanoscale. A scanning probe microscope has been an ideal tool to study the doping effects as well as the superconducting mechanism on these
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