Transport properties and superconductivity in $Ba_{1-x}M_xFe_2As_2$ (M=La and K) with double FeAs layers

TL;DR

This study investigates the transport properties and emergence of superconductivity in Ba-based FeAs compounds with double FeAs layers, revealing doping-dependent carrier type changes and superconducting transition at 38 K.

Contribution

It provides systematic characterization of La and K doping effects on BaFe2As2, highlighting the role of carrier type and structure in superconductivity in double FeAs layer compounds.

Findings

Potassium doping induces superconductivity at 38 K.

Carrier type switches from n-type to p-type with K doping.

Superconductivity observed in Ba-K-Fe-As with double FeAs layers.

Abstract

We synthesized the samples $Ba_{1-x}M_xFe_2As_2$ (M=La and K) with $ThCr_2Si_2$-type structure. These samples were systematically characterized by resistivity, thermoelectic power (TEP) and Hall coefficient ($R_H$). $BaFe_2As_2$ shows an anomaly in resistivity at about 140 K. Substitution of La for Ba leads to a shift of the anomaly to low temperature, but no superconducting transition is observed. Potassium doping leads to suppression of the anomaly in resistivity and induces superconductivity at 38 K as reported by Rotter et al.\cite{rotter}. The Hall coefficient and TEP measurements indicate that the TEP is negative for $BaFe_2As_2$ and La-doped $BaFe_2As_2$, indicating n-type carrier; while potassium doping leads to change of the sign in $R_H$ and TEP. It definitely indicates p-type carrier in superconducting $Ba_{1-x}K_xFe_2As_2$ with double FeAs layers, being in contrast to the case of $LnO_{1-x}F_xFeAs$ with single FeAs layer. A similar superconductivity is also observed in the sample with nominal composition $Ba_{1-x}K_xOFe_2As_2$.