Nodeless multiband superconductivity in stoichiometric single crystalline CaKFe$_4$As$_4$

Kyuil Cho; A. Fente; S. Teknowijoyo; M. A. Tanatar; T. Kong; W. Meier; U. Kaluarachchi; I. Guillamón; H. Suderow; S. L. Bud'ko; P. C. Canfield; R. Prozorov

doi:10.1103/physrevb.95.100502

arXiv · 1606.06245

Nodeless multiband superconductivity in stoichiometric single crystalline CaKFe$_4$As$_4$

Kyuil Cho·A. Fente·S. Teknowijoyo·M. A. Tanatar·T. Kong·W. Meier·U. Kaluarachchi·I. Guillamón·H. Suderow·S. L. Bud'ko·P. C. Canfield·R. Prozorov

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Abstract

Measurements of the London penetration depth and tunneling conductance in single crystals of the recently discovered stoicheometric, iron - based superconductor, CaKFe$_4$As$_4$ (CaK1144) show nodeless, two effective gap superconductivity with a larger gap of about 6-9 meV and a smaller gap of about 1-4 meV. Having a critical temperature, $T_{c,onset}\approx$35.8 K, this material behaves similar to slightly overdoped Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ (e.g. $x=$0.54, $T_c \approx$ 34 K)---a known multigap $s_{\pm}$ superconductor. We conclude that the superconducting behavior of stoichiometric CaK1144 demonstrates that two-gap $s_{\pm}$ superconductivity is an essential property of high temperature superconductivity in iron - based superconductors, independent of the degree of substitutional disorder.

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Kyuil Cho, A. Fente, S. Teknowijoyo, M. A. Tanatar, T. Kong, W. Meier, U. Kaluarachchi, I. Guillamón, H. Suderow, S. L. Bud'ko, P. C. Canfield, R. Prozorov. 2016-06-20. Nodeless multiband superconductivity in stoichiometric single crystalline CaKFe$_4$As$_4$. https://doi.org/10.1103/physrevb.95.100502

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