Physics and Astronomy, Ames Laboratory
Journal or Book Title
Physical Review B
Single-crystalline, single-phase CaKFe 4 As 4 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 CaKFe 4 As 4 is an ordered, stoichiometric, Fe-based superconductor with a superconducting critical temperature, T c = 35.0 ± 0.2 K. Other than superconductivity, there is no indication of any other phase transition for 1.8 K ≤ T ≤ 300 K. All of these thermodynamic and transport data reveal striking similarities to those found for optimally or slightly overdoped ( Ba 1 − x K x ) Fe 2 As 2 , suggesting that stoichiometric CaKFe 4 As 4 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, H c 2 ( T ) , of CaKFe 4 As 4 was determined up to 630 kOe. The anisotropy parameter γ ( T ) = H ⊥ c 2 / H ∥ c 2 , for H applied perpendicular and parallel to the c axis, decreases from ≃ 2.5 at T c to ≃ 1.5 at 25 K, which can be explained by interplay of paramagnetic pair breaking and orbital effects. The slopes of d H ∥ c 2 / d T ≃ − 44 kOe/K and d H ⊥ c 2 / d T ≃ − 109 kOe/K at T c yield an electron mass anisotropy of m ⊥ / m ∥ ≃ 1 / 6 and short Ginzburg-Landau coherence lengths ξ ∥ ( 0 ) ≃ 5.8 Å and ξ ⊥ ( 0 ) ≃ 14.3 Å . The value of H ⊥ c 2 ( 0 ) can be extrapolated to ≃ 920 kOe, well above the BCS paramagnetic limit.
American Physical Society
Meier, William R.; Kong, Tai; Kaluarachchi, Udhara S.; Taufour, Valentin; Jo, Na Hyun; Drachuck, Gil; Böhmer, Anna E.; Saunders, Scott M.; Sapkota, Aashish; Kreyssig, Andreas; Tanatar, Makariy A.; Prozorov, Ruslan; Goldman, Alan I.; Balakirev, Fedor F.; Gurevich, Alex; Bud’ko, Sergey L.; and Canfield, Paul C., "Anisotropic thermodynamic and transport properties of single-crystalline CaKFe4As4" (2016). Physics and Astronomy Publications. 568.