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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$_{x}$Fe$_{2}$As$_{2}$. Using electrical transport, elastic neutron scattering and resonant tunnel diode oscillator measurements on samples under both quasi-hydrostatic 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) quantum critical point. Our results indicate that the observed superconducting phase with 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. In contrast to all other intermetallic iron-pnictide superconductors with the ThCr$_2$Si$_2$ structure, this superconducting phase appears to exist only exclusively from the antiferromagnetic phase in a manner similar to the oxygen- and fluorine-based iron-pnictide superconductors with the highest transition temperatures reported to date. The unusual dichotomy between lower-$T_{c}$ systems with coexistent superconductivity and magnetism and the tendency for the highest-$T_{c}$ systems to show non-coexistence provides an important insight into the distinct transition temperature limits in different members of the iron-based superconductor family.
We report measurements of the pressure dependence of the superconducting transition temperature T_c in single crystal samples of the rare-earth doped superconductor Ca$_{0.73}$La$_{0.27}$Fe$_2$As$_2$. We track T_c with two techniques, via in-plane re
The effect of hydrostatic pressure and partial Na substitution on the normal-state properties and the superconducting transition temperature ($T_c$) of K$_{1-x}$Na$_x$Fe$_2$As$_2$ single crystals were investigated. It was found that a partial Na subs
We prepared the samples K$_{1-x}$Ln$_{x}$Fe$_2$As$_2$ (Ln=Sm, Nd and La) with ThCr$_2$Si$_2$-type structure. These samples were characterized by X-ray diffraction, resistivity, susceptibility and thermoelectric power (TEP). Substitution of Ln (Ln=La,
We measured the in-plane resistivity anisotropy in the underdoped Ca$_{1-x}$Na$_x$Fe$_2$As$_2$ single crystals. The anisotropy (indicated by $rho_{rm b} - rho_{rm a}$) appears below a temperature well above magnetic transition temperature $T_{rm N}$,
Using electronic Raman spectroscopy, we report direct measurements of charge nematic fluctuations in the tetragonal phase of strain-free Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ single crystals. The strong enhancement of the Raman response at low temperatu