Crystal growth and pressure effect on the transport properties in 122-type (La,Na,K)Fe2As2 superconductors

Abstract High-quality single crystals are essential for probing the intrinsic properties of unconventional superconductors. In this work, we report the successful growth of (La,Na,K)Fe2As2 single crystals, a novel 122-type iron-based superconductor, using the self-flux method. The crystal structure and chemical composition were characterized through x-ray diffraction and energy-dispersive x-ray spectroscopy. The (La,Na,K)Fe2As2 single crystals exhibit bulk superconductivity, with a critical transition temperature Tc of approximately 22 K. Magnetization measurements reveal a second peak effect and a critical current density Jc ~ 5×105 A/cm2 at 2 K in a self-field. The upper critical field anisotropy was systematically studied within the framework of the anisotropic Ginzburg–Landau theory, yielding an anisotropy value of approximately 2.6. Furthermore, we employ the diamond anvil cell technique to investigate the pressure effect on (La,Na,K)Fe2As2. Our results demonstrate that superconductivity is gradually suppressed with increasing pressure, while the normal state resistivity at low temperatures evolves from non-Fermi liquid to Fermi liquid behavior. This observation suggests that (La,Na,K)Fe2As2 may be situated on the right of the quantum critical point or, at the very least, within the over-doped region. These findings provide a critical sample platform and experimental insights for advancing the understanding of the physical properties of the newly discovered (La,Na,K)Fe2As2 superconductors.