We have studied ${\mathrm{EuFe}}_2({\mathrm{As}}_{0.7}{\mathrm{P}}_{0.3}{)}_2$ by the measurements of x-ray diffraction, electrical resistivity, thermopower, magnetic susceptibility, magnetoresistance, and specific heat. Partial substitution of As with P results in the shrinkage of lattice, which generates chemical pressure to the system. It is found that ${\mathrm{EuFe}}_2({\mathrm{As}}_{0.7}{\mathrm{P}}_{0.3}{)}_2$ undergoes a superconducting transition at 26 K, followed by ferromagnetic ordering of ${\mathrm{Eu}}^{2+}$ moments at 20 K. This finding is the first observation of superconductivity stabilized by internal chemical pressure, and supplies a rare example showing the coexistence of superconductivity and ferromagnetism in the ferroarsenide family.

We report the discovery of bulk superconductivity (SC) at 6.1 K in a quasi-one-dimensional chromium pnictide ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ that contains $[({\mathrm{Cr}}_3{\mathrm{As}}_3{)}^{2-}{]}_{\infty }$ double-walled subnanotubes with face-sharing ${\mathrm{Cr}}_{6/2}$ (${\mathrm{As}}_{6/2}$) octahedron linear chains in the inner (outer) wall. The material has a large electronic specific-heat coefficient of $70–75\mathrm{mJ}{\mathrm{K}}^{-2}{\mathrm{mol}}^{-1}$, indicating significantly strong electron correlations. A linear temperature dependence of resistivity in a broad temperature range from 7 to 300 K is observed, which suggests non-Fermi liquid behavior of the material. Unconventional SC is preliminarily manifested by the estimated upper critical field exceeding the Pauli limit by a factor of 3–4. The title compound represents a rare example that possibly unconventional SC emerges in a quasi-1D system with strong electron correlations.

A series of 122 phase BaFe$_{2-x}$Ni$_x$As$_2$ ($x$ = 0, 0.055, 0.096, 0.18, 0.23) single crystals were grown by self flux method and a dome-like Ni doping dependence of superconducting transition temperature is discovered. The transition temperature $T_c^{on}$ reaches a maximum of 20.5 K at $x$ = 0.096, and it drops to below 4 K as $x$ $\geq$ 0.23. The negative thermopower in the normal state indicates that electron-like charge carrier indeed dominates in this system. This Ni-doped system provides another example of superconductivity induced by electron doping in the 122 phase.

Following the discovery of superconductivity in quasi-one-dimensional ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ containing ${\left[{\left({\text{Cr}}_3{\mathrm{As}}_3\right)}^{2-}\right]}_{\infty }$ chains (J. K. Bao et al., arXiv:1412.0067), we succeeded in synthesizing an analogous compound, ${\mathrm{Rb}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$, which also crystallizes in a hexagonal lattice. The replacement of K by Rb results in an expansion of the $a$ axis by 3%, indicating a weaker interchain coupling in ${\mathrm{Rb}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$. Bulk superconductivity emerges at 4.8 K, above which the normal-state resistivity shows a linear temperature dependence up to 35 K. The estimated upper critical field at zero temperature exceeds the Pauli paramagnetic limit by a factor of 2. Furthermore, the electronic specific-heat coefficient extrapolated to zero temperature in the mixed state increases with $\sqrt{H}$, suggesting the existence of nodes in the superconducting energy gap. Hence ${\mathrm{Rb}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ manifests itself as another example of an unconventional superconductor in the ${\mathrm{Cr}}_3{\mathrm{As}}_3$-chain based system.

Ternary iron arsenide ${\text{EuFe}}_2{\text{As}}_2$ with ${\text{ThCr}}_2{\text{Si}}_2$-type structure has been studied by magnetic susceptibility, resistivity, thermopower, Hall, and specific-heat measurements. The compound undergoes two magnetic phase transitions at about 200 and 20 K, respectively. The former was found to be accompanied with a slight drop in magnetic susceptibility (after subtracting the Curie-Weiss paramagnetic contribution), a rapid decrease in resistivity, a large jump in thermopower, and a sharp peak in specific heat with decreasing temperature, all of which point to a spin-density-wave-like antiferromagnetic transition. The latter was proposed to be associated with an $A$-type antiferromagnetic ordering of ${\text{Eu}}^{2+}$ moments. Comparing with the physical properties of the isostructural compounds ${\text{BaFe}}_2{\text{As}}_2$ and ${\text{SrFe}}_2{\text{As}}_2$, we expect that superconductivity could be induced in ${\text{EuFe}}_2{\text{As}}_2$ through appropriate doping.