Anisotropic physical properties and large critical current density in KCa2Fe4As4F2 single crystal

We present a systematic study of electrical resistivity, Hall coefficient, magneto-optical imaging, magnetization, and scanning transmission electron microscopy (STEM) analyses of KCa2Fe4As4F2 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 J(c) suggest that the electronic state is quasi-two-dimensional. Hall effect measurements indicate that KCa2Fe4As4F2 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. The origin of these J(c) characteristics is discussed based on microstructural observations using STEM. In addition, further enhancement of J(c) in KCa2Fe4As4F2 for future high-field application is demonstrated in terms of heavy-ion irradiation.