Separation of antiferromagnetism and high-temperature superconductivity in Ca$_{1-x}$La$_x$Fe$_2$As$_2$ under pressure

摘要

We report the effect of applied pressures on magnetic and superconductingorder in single crystals of the aliovalent La-doped iron pnictide materialCa$_{1-x}$La$_{x}$Fe$_{2}$As$_{2}$. Using electrical transport, elastic neutronscattering and resonant tunnel diode oscillator measurements on samples underboth quasi-hydrostatic and hydrostatic pressure conditions, we report a seriesof phase diagrams spanning the range of substitution concentrations for bothantiferromagnetic and superconducting ground states that includepressure-tuning through the antiferromagnetic (AFM) quantum critical point. Ourresults indicate that the observed superconducting phase with maximumtransition temperature of $T_{c}$=47 K is intrinsic to these materials,appearing only upon suppression of magnetic order by pressure tuning throughthe AFM critical point. In contrast to all other intermetallic iron-pnictidesuperconductors with the ThCr$_2$Si$_2$ structure, this superconducting phaseappears to exist only exclusively from the antiferromagnetic phase in a mannersimilar to the oxygen- and fluorine-based iron-pnictide superconductors withthe highest transition temperatures reported to date. The unusual dichotomybetween lower-$T_{c}$ systems with coexistent superconductivity and magnetismand the tendency for the highest-$T_{c}$ systems to show non-coexistenceprovides an important insight into the distinct transition temperature limitsin different members of the iron-based superconductor family.