Ferromagnetism and Superconductivity in LiFeAs

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LiFeAs is radically different from the canonical iron-arsenide superconductors, where strong nesting between hole-like and electron-like Fermi surface (FS) pockets causes an antiferromagnetic spin density wave (SDW) ground state in the undoped parent compounds. Superconductivity emerges already without doping, at a relatively high critical temperature of about 18K. The FS of LiFeAs is poorly nested and the topf of two hole-like bands at the Gammapoint almost touch the Fermi level yielding a structure close to a van-Hove singularity. Our prelminiary data show ferromagnetism in Li deficient LiFeAs, i.e. LiFeAs is a pnictide superconductor close to a ferromagnetic phase. The determination and interpretation of the electronic phase diagram including the change from ferromagnetism to superconductivity and the investigation of consequences of the proximity of these two competing states are the central objectives of this project. These challenging task will be tackled by a combination of experimental and theoretical efforts.