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Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals

S. Teknowijoyo, K. Cho, M. A. Tanatar, J. Gonzales, A. E. Böhmer, O. Cavani, V. Mishra, P. J. Hirschfeld, S. L. Bud'ko, P. C. Canfield, R. Prozorov

DOI 10.1103/PhysRevB.94.064521 · Physical Review B

T1

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Abstract

A highly anisotropic superconducting gap is found in single crystals of FeSe by studying the London penetration depth Δλ measured down to 50 mK in samples before and after 2.5 MeV electron irradiation. The gap minimum increases with introduced pointlike disorder, indicating the absence of symmetry-imposed nodes. Surprisingly, the superconducting transition temperature Tc increases by 0.4 K from Tc0≈8.8 K while the structural transition temperature Ts decreases by 0.9 K from Ts0≈91.2 K after electron irradiation. We discuss several explanations for the Tc enhancement and propose that local strengthening of the pair interaction by irradiation-induced Frenkel defects most likely explains the phenomenon.

Source-reported materials — not catalogue approval

FormulaReported Tc (K)Pressure (GPa)Type
FeSe

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8.8Pressure unresolvedmidpoint
FeSe

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9.2Pressure unresolvedmidpoint
FeSe

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65Pressure not reportedunknown
BaFe2(As,P)2

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—Pressure not reportedunknown
SrFe2(As,P)2

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—Pressure not reportedunknown

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