Superconductivity in the layered compound Li_xNbO₂

Abstract

SEVERAL classes of copper oxide compounds are high-temperature superconductors^1–3; the highest known transition temperature (T_c) is 122 K for Tl₂Ba₂Ca₂Cu₃O₁₁ (ref. 4). Superconductivity has also been observed in oxides containing early transition metals, but the superconducting transition temperatures are substantially lower. (The highest known T_c for an early transition metal oxide is 13.7 K, for the spinel compound LiTi₂O₄ (ref. 5).) Whereas all of the copper oxide superconductors have very anisotropic structures, the superconducting oxides of early transition metals discovered up to now have three-dimensional structures. Here we report the discovery of a new class of superconductors, Li_xNbO₂ with layered structures. At low applied magnetic fields, the magnetic susceptibility greatly decreases to diamagnetic values below 5.5 K for Li_0.45NbO₂ and below 5.5 K for Li_0.45NbO₂; this transition indicates the onset of superconductivity. In this first example of superconductivity in a layered early transition metal oxide, it is interesting to note that the layering has not increased T_c to new levels for early transition metal oxides.