Increased critical current density in iron selenide telluride crystals doping with trace amount of cobalt

Iron selenide telluride superconductors, succeeding copper oxide superconductors, have refuted the long-standing belief that superconductors are incompatible with ferromagnetic elements. Moreover, their pronounced sensitivity to chemical doping offers a distinct advantage for the investigation of superconductivity mechanisms, thereby enriching the academic discourse in the field. This study employed a self-flux method to synthesize CoxFe1−xSe0.4Te0.6 crystals with trace cobalt (Co) doping at levels below 1%. Extensive structural elucidation and low-temperature physical property assessments have been conducted on the doped crystals, providing a detailed understanding of their material properties and behavior under cryogenic conditions. Our findings revealed that trace Co doping enhances the critical current density under high magnetic fields. Utilizing the Dew-Hughes model, we quantitatively assessed the pinning force and determined that Co doping effectively modulates it, corroborating the observed enhancement in critical current density. These insights advance our understanding of the role of dopants in iron-based superconductors and offer significant theoretical underpinnings for the development of high-performance iron-based superconducting materials.