Tao Xie

Crystal growth and phase diagram of 112-type iron pnictide superconductor Ca1−y La y Fe1−x Ni x As2

We report a systematic crystal growth and characterization of Ca1−y La y Fe1−x Ni x As2, the newly discovered 112-type iron-based superconductor. After substituting Fe by a small amount of Ni, bulk superconductivity is successfully obtained in high-quality single crystals sized up to 6 mm. Resistivity measurements indicate common features for transport properties in this 112-type iron pnictide, suggest strong scattering from chemical dopants. Together with the superconducting transition temperature T c , and the Neel temperature T N determined by the elastic neutron scattering, we sketch a three-dimensional phase diagram in the combination of both Ni and La dopings.

Unified Phase Diagram for Iron-Based Superconductors.

High-temperature superconductivity is closely adjacent to a long-range antiferromagnet, which is called a parent compound. In cuprates, all parent compounds are alike and carrier doping leads to superconductivity, so a unified phase diagram can be drawn. However, the properties of parent compounds for iron-based superconductors show significant diversity and both carrier and isovalent dopings can cause superconductivity, which casts doubt on the idea that there exists a unified phase diagram for them. Here we show that the ordered moments in a variety of iron pnictides are inversely proportional to the effective Curie constants of their nematic susceptibility. This unexpected scaling behavior suggests that the magnetic ground states of iron pnictides can be achieved by tuning the strength of nematic fluctuations. Therefore, a unified phase diagram can be established where superconductivity emerges from a hypothetical parent compound with a large ordered moment but weak nematic fluctuations, which suggests that iron-based superconductors are strongly correlated electron systems.

Quasi-two-dimensional behavior of 112-type iron-based superconductors

Fluctuation magnetoconductivity and magnetization above the superconducting transition temperature (

Nematic Quantum Critical Fluctuations in BaFe2-xNixAs2

{T}_{c}

Nature of the antiferromagnetic and nematic transitions in Sr1−xBaxFe1.97Ni0.03As2

) are measured on the recently discovered 112 family of iron-based superconductors (IBS),

Electronic specific heat inBaFe2−xNixAs2

{\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{Fe}}_{1\ensuremath{-}y}{\mathrm{Ni}}_{y}{\mathrm{As}}_{2}

Electronic specific heat in BaFe2−xNixAs2

, which presents an extra As-As chain spacer-layer. The analysis in terms of a generalization of the Lawrence-Doniach approach to finite applied magnetic fields indicates that these compounds are among the most anisotropic IBS (

Electronic specific heat in BaFe

\ensuremath{\gamma}

_{2-x}

up to

Ni

\ensuremath{\sim}30