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We present a systematic study of electrical resistivity, Hall coefficient, magneto-optical imaging, magnetization, and STEM analyses of KCa${_2}$Fe${_4}$As${_4}$F${_2}$ single crystals. Sharp diamagnetic transition and magneto-optical imaging reveal homogeneity of single crystal and prominent Bean-like penetrations of vortices. Large anisotropy of electrical resistivity, with ${rho _c / rho _{ab}}$ > 100, and semiconductor-like ${rho _c}$ suggest that the electronic state is quasi two-dimensional. Hall effect measurements indicate that KCa${_2}$Fe${_4}$As${_4}$F${_2}$ is a multiband system with holes as main carriers. Magnetization measurements reveal significantly larger J$_c$ compared with that in other iron-based superconductors with different values of J$_c$ depending on the direction of magnetic field. Origin of these J$_c$ characteristics is discussed based on microstructural observations using STEM. In addition, further enhancement of J$_c$ in KCa${_2}$Fe${_4}$As${_4}$F${_2}$ for future application is demonstrated in terms of heavy-ion irradiation.
We find evidence that the newly discovered Fe-based superconductor KCa$_2$Fe$_4$As$_4$F$_2$ ($T_c~=~33.36(7)$~K) displays multigap superconductivity with line nodes. Transverse field muon spin rotation ($mu$SR) measurements show that the temperature
We report synthesis, crystal structure and physical properties of a quinary iron-arsenide fluoride KCa$_2$Fe$_4$As$_4$F$_2$. The new compound crystallizes in a body-centered tetragonal lattice (with space group $I4/mmm$, $a$ = 3.8684(2) {AA}, c = 31.
Recently, 12442 system of Fe-based superconductors has attracted considerable attention owing to its unique double-FeAs-layer structure. A steep increase in the in-plane upper critical field with cooling has been observed near the superconducting tra
We report resistance and elastoresistance measurements on (Ba$_{0.5}$K$_{0.5}$)Fe$_2$As$_2$, CaKFe$_4$As$_4$, and KCa$_2$Fe$_4$As$_4$F$_2$. The Fe-site symmetry is $D_{2d}$ in the first compound but $C_{2v}$ in the latter two, which lifts the degener
CsCa$_2$Fe$_4$As$_4$F$_2$ is a newly discovered iron-based superconductor with $T_mathrm{c}sim$ 30 K containing double Fe$_2$As$_2$ layers that are separated by insulating Ca$_2$F$_2$ spacer layers. Here we report the transport and magnetization meas