Superconductivity of underdoped PrFeAs(O,F) investigated via point-contact spectroscopy and nuclear magnetic resonance

Abstract

Underdoped PrFeAs(O,F), one of the less known members of the 1111 family of iron-based superconductors, was investigated in detail by means of transport, SQUID magnetometry, nuclear magnetic resonance (NMR) measurements and point-contact Andreev-reflection spectroscopy (PCARS). PCARS measurements on single crystals evidence the multigap nature of PrFeAs(O,F) superconductivity, shown to host at least two isotropic gaps, clearly discernible in the spectra, irrespective of the direction of current injection (i.e., along the ab planes or along the c axis). Additional features at higher energy can be interpreted as signatures of a strong electron-boson coupling, as demonstrated by a model which combines Andreev reflection with the Eliashberg theory. Magnetic resonance measurements in the normal phase indicate the lack of a magnetic order in underdoped PrFeAs(O,F), while ${}^{75}$As NMR spin-lattice relaxation results suggest the presence of significant electronic spin fluctuations, peaking above $T_c$ and expected to mediate the superconducting pairing.

arXiv comment12 pages, 9 figures. Title changed, minor amendments in the text

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• Spectroscopic studies of the superconducting gap in the 12442 family of iron-based compounds
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• Unusually weak irradiation effects in anisotropic iron-based superconductor RbCa2Fe4As4F2
• Direct observation of the spin exciton in Andreev spectroscopy of iron-based superconductors
• High-pressure self-flux growth and characterization of Li-deficient Li0.95FeAs single crystals
• Complete electronic phase diagram and enhanced superconductivity in fluorine-doped PrFeAsO1-xFx
• Superconductivity of Co-Doped CaKFe4As4 Investigated via Point-Contact Spectroscopy and London Penetration Depth Measurements
• Vortex matter and strong pinning in underdoped PrFeAs(O,F) with atomic-sized defects
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