Transport properties and superconductivity in Ba1-xMxFe2As2 (M=La and K) with double FeAs layers

We synthesized the samples Ba1-xMxFe2As2 (M = La and K) with a ThCr2Si2- type structure. These samples were systematically characterized by resistivity, thermoelectric power (TEP) and Hall coefficient (RH). BaFe2As2 shows an anomaly in resistivity at about 140 K. The 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 the suppression of the anomaly in resistivity and induces superconductivity at 38 K. The Hall coefficient and TEP measurements indicate that the TEP is negative for BaFe2As2 and La-doped BaFe2As2, indicating an n-type carrier; while potassium doping leads to a change of the sign in RH and TEP. It definitely indicates a p-type carrier in the superconducting Ba1-xKxFe2As2 with double FeAs layers, being in contrast to the case of LnO1-xFxFeAs with a single FeAs layer.