Superconductivity in the ferromagnetic semiconductor samarium nitride

摘要

Conventional wisdom expects that making semiconductors ferromagnetic requires doping with magnetic ions and that superconductivity cannot coexist with magnetism. However, recent concerted efforts exploring new classes of materials have established that intrinsic ferromagnetic semiconductors exist and that certain types of strongly correlated metals can be ferromagnetic and superconducting at the same time. Here we show that the trifecta of semiconducting behavior, ferromagnetism, and superconductivity can be achieved in a single material. Samarium nitride (SmN) is a well-characterized intrinsic ferromagnetic semiconductor, hosting strongly spin-ordered 4f electrons below a Curie temperature of 27 K. We have now observed that it also hosts a superconducting phase below 4 K when doped to electron concentrations above 10(21) cm(-3). The large exchange splitting of the conduction band in SmN favors equal-spin triplet pairing with p-wave symmetry. Significantly, superconductivity is enhanced in superlattices of gadolinium nitride (GdN) and SmN. An analysis of the robustness of such a superconducting phase against disorder leads to the conclusion that the 4f bands are crucial for superconductivity, making SmN a heavy-fermion-type superconductor.