Document Type


Publication Date




Publication Title

Physical Review B






064501 (1-12)


Single-crystalline, single-phase CaKFe4As4 has been grown out of a high-temperature, quaternary melt. Temperature-dependent measurements of x-ray diffraction, anisotropic electrical resistivity, elastoresistivity, thermoelectric power, Hall effect, magnetization, and specific heat, combined with field-dependent measurements of electrical resistivity and field and pressure-dependent measurements of magnetization indicate that CaKFe4As4 is an ordered, stoichiometric, Fe-based superconductor with a superconducting critical temperature, Tc = 35.0 ± 0.2 K. Other than superconductivity, there is no indication of any other phase transition for 1.8K ≤ T ≤ 300 K. All of these thermodynamic and transport data reveal striking similarities to those found for optimally or slightly overdoped (Ba1−xKx)Fe2As2, suggesting that stoichiometric CaKFe4As4 is intrinsically close to what is referred to as “optimal-doped” on a generalized, Fe-based superconductor, phase diagram. The anisotropic superconducting upper critical field, Hc2(T), of CaKFe4As4 was determined up to 630 kOe. The anisotropy parameter γ(T) = H⊥c2/H∥c2, for H applied perpendicular and parallel to the c axis, decreases from ≃ 2.5 at Tc to ≃1.5 at 25 K, which can be explained by interplay of paramagnetic pair breaking and orbital effects. The slopes of dH∥c2/dT ≃ −44 kOe/K and dH⊥c2/dT ≃ −109 kOe/K at Tc yield an electron mass anisotropy of m⊥/m∥ ≃ 1/6 and short Ginzburg-Landau coherence lengths ξ∥(0) ≃ 5.8Å and ξ⊥(0) ≃ 14.3Å. The value of H⊥c2(0) can be extrapolated to ≃920 kOe, well above the BCS paramagnetic limit.


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Original Publication Citation

Meier, W. R., Kong, T., Kaluarachchi, U. S., Taufour, V., Jo, N. H., Drachuck, G., Böhmer, A. E., Saunders, S. M., Sapkota, A., Kreyssig, A., Tanatar, M. A., Prozorov, R., Goldman, A. I., Balakirev, F. F., Gurevich, A., Bud'ko, S. L., & Canfield, P. C. (2016). Anisotropic thermodynamic and transport properties of single-crystalline CaKFe4As4. Physical Review B, 94(6), 1-12, Article 064501.


0000-0003-0759-8941 (Gurevich)