Enhancement of Tc by point-like disorder and anisotropic gap in FeSe

Abstract

A highly anisotropic superconducting gap is found in single crystals of FeSe by studying the London penetration depth, $\Delta \lambda$, measured down to 50 mK in samples before and after 2.5 MeV electron irradiation. The gap minimum increases with introduced point - like disorder, indicating the absence of symmetry - imposed nodes. Surprisingly, the superconducting transition temperature, $T_c$, \textit{increases} by 0.4 K from $T_{c0}\approx$ 8.8 K while the structural transition temperature, $T_s$, \textit{decreases} by 0.9 K from $T_{s0}\approx$91.2 K after electron irradiation. We discuss several explanations for the $T_c$ enhancement, and propose that local strengthening of the pair interaction by irradiation-induced Frenkel defects most likely explains the phenomenon.

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• Nematicity, magnetism and superconductivity in FeSe
• Orbital selective pairing and gap structures of iron-based superconductors
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• Superconducting gap structure of FeSe
• Disorder raises the critical temperature of a cuprate superconductor
• Single-gap superconductivity and dome of superfluid density in Nb-doped SrTiO3
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• Impact of Disorder on the Superconducting Phase Diagram in BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$
• Itinerant approach to magnetic neutron scattering of FeSe: effect of orbital selectivity
• Imaging anisotropic vortex dynamics in FeSe
• Effects of heavy-ion irradiation on FeSe
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• The drastic effect of the impurity scattering on the electronic and superconducting properties of Cu-doped FeSe
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