Transition of stoichiometric ${\text{Sr}}_2{\text{VO}}_3\text{FeAs}$ to a superconducting state at 37.2 K

The superconductor ${\text{Sr}}_4{\text{V}}_2{\text{O}}_6{\text{Fe}}_2{\text{As}}_2$ with transition temperature at 37.2 K was successfully fabricated. It has a layered structure with the space group of $p4/nmm$ and with the lattice constants $a=3.9296\text{Å}$ and $c=15.6732\text{Å}$. The observed large diamagnetization signal and zero resistance demonstrated the bulk superconductivity. The broadening of resistive transition was measured under different magnetic fields revealing a rather high upper critical field. The results also suggest a large vortex liquid region that reflects high anisotropy of the system. The Hall-effect measurements revealed dominantly electronlike charge carriers in this material. The superconductivity in the present system may be induced by oxygen deficiency or the multiple valence states of vanadium.

Figure 1

(Color online) x-ray diffraction patterns for the sample ${\text{Sr}}_4{\text{V}}_2{\text{O}}_6{\text{Fe}}_2{\text{As}}_2$. Bottom: ${\text{Sr}}_2{\text{VO}}_4$ was included in the refinement as the minor impurity phase.

Figure 2

(Color online) (a) Temperature dependence of the dc susceptibility for the sample ${\text{Sr}}_4{\text{V}}_2{\text{O}}_6{\text{Fe}}_2{\text{As}}_2$. The dc susceptibility data were obtained using the zero-field-cooling and field-cooling modes with a dc magnetic field of 10 Oe. The onset superconducting transition temperature was determined to be 31.5 K. (b) Temperature dependence of the resistivity under zero field in temperature region up to 300 K.

Figure 3

(Color online) (a) Temperature dependence of resistivity in the low-temperature region under different fields. The onset transition temperature was determined to be 37.2 K in the data under zero field. (b) The phase diagram plotted as $H_{c2}$ versus $T$. A criterion of 90% ${\rho }_n$ was taken to determine the upper critical fields. The irreversibility line $H_{irr}$ taking with the criterion of 0.1% ${\rho }_n$ is also presented in this figure.

Figure 4

(Color online) Temperature dependence of Hall coefficient $R_H\left(T\right)$ determined at 9 T from the transverse resistivity ${\rho }_{xy}$ shown in the inset. It is clear that the transverse resistivity ${\rho }_{xy}$ is negative and linearly related to the magnetic field, suggesting that the electron conduction is dominated by the electronlike charge carriers in ${\text{Sr}}_4{\text{V}}_2{\text{O}}_6{\text{Fe}}_2{\text{As}}_2$.