Evidence for charge and spin density waves in single crystals of La 3 Ni 2 O 7 and La 3 Ni 2 O 6

Charge and spin orders are intimately related to superconductivity in copper oxide superconductors. Elucidation of the competing orders in various nickel oxide compounds is crucial, given the fact that superconductivity has been discovered in Nd 0.8 Sr 0.2 NiO 2 films. Herein, we report structural, electronic transport, magnetic, and thermodynamic characterizations of single crystals of La 3 Ni 2 O 7 and La 3 Ni 2 O 6 . La 3 Ni 2 O 7 is metallic with mixed Ni 2+ and Ni 3+ valent states. Resistivity measurements yield two transition-like kinks at ∼ 110 and 153 K. The kink at 153 K is further revealed from magnetization and specific heat measurements, indicative of the formation of charge and spin density waves. La 3 Ni 2 O 6 single crystals obtained from the topochemical reduction of La 3 Ni 2 O 7 are insulating and show an anomaly at ∼176 K on magnetic susceptibility. The transition-like behaviors of La 3 Ni 2 O 7 and La 3 Ni 2 O 6 are analogous to those observed in La 4 Ni 3 O 10 and La 4 Ni 3 O 8 , suggesting that charge and spin density waves are a common feature in the ternary La−Ni−O system with mixed-valent states of nickel.