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arXiv · 1605.04170

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

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
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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 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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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. 2016-05-13. Enhancement of Tc by point-like disorder and anisotropic gap in FeSe. https://doi.org/10.1103/physrevb.94.064521

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