Ferromagnetism and Superconductivity in LiFeAs

LIFEAS与经典的砷化铁超导体有根本的不同，在典型的砷化铁超导体中，类空穴和类电子的费米面(FS)口袋之间的强烈嵌套导致未掺杂母体化合物中的反铁磁自旋密度波(SDW)基态。超导电性已经在没有掺杂的情况下出现了，临界温度相对较高，约为18K。Lifeas的FS嵌套得很差，Gammapint处两个类空穴带的顶部几乎触及费米能级，产生了接近van-Hove奇点的结构。我们的初步数据表明，在缺Li的LiVe中存在铁磁性，即LifeAs是一个接近铁磁相的粒子超导体。确定和解释电子相图，包括从铁磁性到超导电性的变化，以及研究这两个相互竞争的状态接近的后果是这个项目的中心目标。这些具有挑战性的任务将通过实验和理论相结合的努力来解决。

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.