Segregation of antiferromagnetism and high-temperature superconductivity in Ca_(1-x)La_xFe_2As_2

摘要

We report the effect of applied pressures on magnetic and superconducting order in single crystals of the aliovalent La-doped iron pnictide material Ca_(1-x)La_xFe_2As_2. Using electrical transport, elastic neutron scattering, and resonant tunnel diode oscillator measurements on samples under both quasihydrostatic and hydrostatic pressure conditions, we report a series of phase diagrams spanning the range of substitution concentrations for both antiferromagnetic and superconducting ground states that include pressure-tuning through the antiferromagnetic (AFM) superconducting critical point. Our results indicate that the observed superconducting phase with a maximum transition temperature of T_c = 47 K is intrinsic to these materials, appearing only upon suppression of magnetic order by pressure-tuning through the AFM critical point. Thus, the superconducting phase appears to exist exclusively in juxtaposition to the antiferromagnetic phase in a manner similar to the oxygen- and fluorine-based iron-pnictide superconductors with the highest transition temperatures reported to date. Unlike the lower- T_c systems, in which superconductivity and magnetism usually coexist, the tendency for the highest-T_c systems to show noncoexistence provides an important insight into the distinct transition temperature limits in different members of the iron-based superconductor family.