硫族和磷族化合物中量子物态和新超导体探索

Transition metal chalcogenides with low diemnsional structure are often found to have charge-density-wave (CDW) ground state and there could exist a competition of superconductivity with CDW. Thus these materials become new avene for exploring new superconductors, and controlling of quantum state. Meanwhile, the discovery of iron-based superconductors made the pnictides the focus of rersearch. Recently the Weyl semimetals were also discovered in the pnictides (such as TaAs, TaP etc). Superconducitivity could be achieved by applying pressure or chemical doping in the topological semimetals, thus they are possible candidates of the topological superconductors. Based on our research experience, this project will further explore superconductivity among the quasi-1D or quasi-2D chalcogenides and pnictides. Combined with band structure calculations, we will design new materials with similar stucture, and tune the ground states by element subsitution or applying pressure or field. We will study the coexistence or competition of superconductivity with other orders in the newly discovered systems, establish the electronic phase diagrams, discover possible quantum criticality, understand the mechanism of superconductivity, and explore possible topological superconductivity.

低维结构的过渡金属硫族化合物往往具有电荷密度波态,与超导态共存或者相互竞争. 通过外界参量(如压力,组分掺杂)的调控,可以压制电荷密度波, 引导或增强超导电性, 使得低维硫族化合物成为寻找新超导体, 调控超导等量子态的新源泉. 同时, 铁基超导体的发现也让层状磷族化合物成为研究的焦点, 近年更发现许多磷族化合物(如TaAs, TaP)也是拓扑半金属材料, 通过加压或者掺杂也能诱发超导电性,成为拓扑超导体的热门候选材料.本项目将在以往研究的基础上进一步探索准一维和准二维硫族和磷族化合物中的超导电性, 结合能带理论计算, 设计相关结构材料,通过元素替代和外场调控发现新的材料体系, 研究超导态与其它有些态共存或竞争的关系, 建立各体系的电子相图, 研究可能的量子临界性,加深对超导机理的理解, 探索可能的拓扑超导电性.

本项目在低维结构硫族或磷族过渡金属化合物中利用掺杂、插层或加压等调控方法获得新的非常规超导体，并进而研究了超导电性与电荷密度波共存和竞争的关系，与拓扑物态共存，发现了潜在的拓扑超导材料。主要成果如下：（1）合成基于2H-(Nb/Ta)Se2结构单元的晶格失配结构的新超导体(SnSe)1.16(NbSe2)和(PbSe)1.12(TaSe2)n (n=1,2)；（2）合成In或Pb插层的新超导体InxTaSe2， InxTaS2, Pb1/3TaS2, 以及高阶插层超导体Pb(TaSe2)2，发现这些超导体系与电荷密度波或拓扑能带等共存，是寻找拓扑超导体的潜在体系；（3）还发现了非中心对称结构的NbGe2第一类超导体，具有Bi四方格子的层状结构超导体Er2O2Bi，在高压下超导的拓扑半金属NbAs2等；（4）在低维的黑砷材料中发现有趣的量子霍尔效应，发现全新的自旋-能谷耦合的Rashba物理现象。已经国际主流刊物发表学术论文30篇。