Synthesis and characterization of the hole-doped nickel-based superconductor La1-xSrxNiAsO

We report the synthesizing and characterization of the hole-doped Ni-based superconductor La1-xSrxNiAsO. By substituting La with Sr, the superconducting transition temperature T-c is increased from 2.4 K of the parent phase LaNiAsO to 3.7 K at the doping levels x=0.1-0.2. The curve Tc versus hole concentration shows a symmetric behavior as the electron-doped samples LaNiAs(O1-xFx). The normal-state resistivity in Ni-based samples shows a good metallic behavior and reveals the absence of a spin-density wave induced anomaly, which appears in the Fe-based system at about 150 K. Hall-effect measurements indicate that the electron conduction in the parent phase LaNiAsO is dominated by electronlike charge carriers, while with more Sr doping, a holelike band will emerge and finally prevail over the conduction. Such a phenomenon reflects that the Fermi surface of LaNiAsO comprises of electron and hole pockets; thus the sign of charge carriers could be changed once the contribution of hole pockets overwhelms that of electron pockets. Magnetoresistance measurements and the violation of the Kohler rule provide further proof that multiband effect dominates the normal-state transport of La1-xSrxNiAsO.