Hole doping in BaFe2As2 The case of Ba1 xNaxFe2As2 single crystals

Single crystals of Ba$_{1-x}$Na$_x$Fe$_2$As$_2$ with $x$ = 0, 0.25, 0.35, 0.4 were grown using a self-flux high temperature solution growth technique. The superconducting and normal state properties were studied by temperature dependent magnetic susceptibility, electrical resistivity and specific heat revealing that the magnetic and structural transition is rapidly suppressed upon Na-substitution at the Ba-site in BaFe$_2$As$_2$, giving rise to superconductivity. A superconducting transition as high as 34 K is reached for a Na-content of $x$=0.4. The positive Hall coefficient confirms that the substitution of Ba by Na results in hole-doping similarly to the substitution of Ba by K. Angle resolved photoemission spectroscopy was performed on all Ba$_{1-x}$Na$_x$Fe$_2$As$_2$ crystals. The Fermi surface of hole-doped Ba$_{1-x}$Na$_x$Fe$_2$As$_2$ is to high extent the same as the Fermi surface found for the K-doped sister compounds, suggesting a similar impact of the substitution of Ba by either K or Na on the electronic band dispersion at the Fermi leve

Co NO3 2 as an inverted umbrella type chiral noncoplanar ferrimagnet

The low dimensional magnetic systems tend to reveal exotic spin liquid ground states or form peculiar types of long range order. Among systems of vivid interest are those characterized by the triangular motif in two dimensions. The realization of either ordered or disordered ground state in triangular, honeycomb, or kagome lattices is dictated by the competition of exchange interactions, also being sensitive to anisotropy and the spin value of magnetic ions. While the low spin Heisenberg systems may arrive to a spin liquid long range entangled quantum state with emergent gauge structures, the high spin Ising systems may establish the rigid noncollinear structures. Here, we present the case of chiral noncoplanar inverted umbrella type ferrimagnet formed in cobalt nitrate Co NO3 2 below TC 3K with the comparable spin and orbital contributions to the total magnetic momen