A New Pnictide Superconductor without Iron

摘要

Soon after the discovery of the new superconductor LaFeAs-n(O1 xFx) of the so-called 1111 series, the superconductive transitionntemperature Tc was optimized from 26 K to ∼55 K by substitutingnother rare-earth ions for La3n; see the review1nand references therein.nWithout changing the basic structural unit supporting supercon-nductivity, i.e. the Fe2X2 layer, several new systems such as LiFeAsn(111),n2nAFe2As2 (A Sr, Ba, and partial potassium substitution fornthese two alkali earths) (122),n3nand FeSe1 δ (11)n4nhave also beennshown to be superconductive. Unlike high-Tc superconductivity innthe perovskite-related copper oxides, substitution on iron sites bynseveral other 3d,4d, and 5d transition metals is not harmful tonthe superconductive phase in the iron-based pnictides;n5nchemicalnsubstitutions on the iron sites are even necessary to inducensuperconductivity in the parent compounds of the 122 systems.nSuperconductivity, however, does not survive if iron is completelynreplaced in these 122 systems. Here we report superconductivitynwith Tc ≈ 3.7 K in a copper-based pnictide LiCu2P2, which has ancrystal structure similar to that of (122) AFe2As2. We have alsonshown superconductivity in another 111 pnictide, LiFeP, with Tcn≈ 4.1 K. These results support a multiband superconductivity innthe pnictides.