Pressure studies on the electrical properties in R_2-xSr_xNi_1-yCu_yO_4+δ(R=La, Nd) and La₃Ni₂O_7+δ

Abstract

The Ruddlesden-Popper series of compounds Lan+1NinO3n+1 are one of the strongly correlated electron systems. Among these compounds, La2NiO4 (n=1) is a well-known two-dimensional antiferromagnetic insulator. Electrical resistivity under high pressure have been measured on R2-xSrxNi1-yCuyO4+δ (R=La, Nd) up to 2 GPa and La3Ni2O7+δ up to ∼20 GPa. Elecrical resistivty of La1.92Sr1.08NiO4 under high pressure reveals an enhancement of the electronic localization under pressure. On the other hand, in case of Nd1.6Sr0.4Ni0.5Cu0.5O4+δ, a metal-insulator transition is observed at ∼240 K and a metallic state is favorable under pressure, in contrast to La1.92Sr1.08NiO4. In La3Ni2O7+δ pressure also enhances a metallic state up to 2 GPa.