Transport properties and superconductivity in BaM_xFe₂As₂ (M=La and K) with double FeAs layers

Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China - Hefei, Anhui 230026, PRC

Corresponding author: chenxh@ustc.edu.cn

Received: 9 June 2008
Accepted: 4 September 2008

Abstract

We synthesized the samples BaM_xFe₂As₂ ( M = La and K) with a ThCr₂Si₂-type structure. These samples were systematically characterized by resistivity, thermoelectric power (TEP) and Hall coefficient (R_H). 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 R_H and TEP. It definitely indicates a p-type carrier in the superconducting BaK_xFe₂As₂ with double FeAs layers, being in contrast to the case of LnOF_xFeAs with a single FeAs layer.