Superconductivity from repulsion in LiFeAs: Novel s-wave symmetry and potential time-reversal symmetry breaking
Superconductivity from repulsion in LiFeAs: Novel s-wave symmetry and potential time-reversal symmetry breaking
复制标题
DOI：
10.1103/physrevb.89.144513
复制
发表时间：
2014-04-25
影响因子：
3.7
通讯作者：
Chubukov, A. V.
中科院分区：
文献类型：
--
作者：
Ahn, F.;Eremin, I.;Chubukov, A. V.
通过将不同k（z）切割下的配对相互作用分解为s波和d波分量，并通过研究主要的超导不稳定性，我们分析了LiFeAs中的配对相互作用和超导能隙的结构。我们使用十轨道紧束缚模型，来自从头计算LDA计算与跳跃参数提取适合ARPES实验。我们发现，配对相互作用几乎是两个子集之间的重叠;一个由外空穴袋和两个电子袋组成，这是准二维的，主要是由d（xy）轨道，另一个由两个内空穴袋组成，这是准三维的，主要是由d（xz）和d（yz）轨道。此外，在每个子集内的裸袋间和袋内相互作用几乎相等。在这种情况下，由于高能费米子的重整化，口袋内和口袋间的相互作用发生了微小的变化，从而产生了各种不同的能隙结构。我们专注于s波配对，实验表明，是最有可能的配对对称性LiFeAs。我们发现四种不同的配置的s波间隙直接低于Tc：其中超导间隙在两个内孔袋之间以及在外孔袋和两个电子袋之间改变符号，其中差距在两个电子袋和三个孔袋之间改变符号，其中外孔袋上的差距在符号上不同于其他四个袋上的间隙，一种是两个内孔袋上的间隙具有一个符号，而外孔袋和电子袋上的间隙具有不同的符号。不同的s-波间隙配置出现取决于是否重整化的相互作用增加每个子集内的吸引力或增加两个子集的特定组件之间的耦合。我们讨论了相图和实验探针，以确定在LiFeAs超导间隙的结构。我们认为，与ARPES数据重叠最好的两个内孔口袋的间隙符号相反的状态。我们还认为，在低T，系统可能进入一个“混合”的s +是状态，在不同的口袋上的间隙的相位相差小于p和时间反演对称性自发破缺。
We analyze the structure of the pairing interaction and superconducting gap in LiFeAs by decomposing the pairing interaction for various k(z) cuts into s-and d-wave components and by studying the leading superconducting instabilities. We use the ten-orbital tight-binding model, derived from ab initio LDA calculations with hopping parameters extracted from the fit to ARPES experiments. We find that the pairing interaction almost decouples between two subsets; one consists of the outer hole pocket and two electron pockets, which are quasi-2D and are made largely out of the d(xy) orbital, and the other consists of the two inner hole pockets, which are quasi-3D and are made mostly out of d(xz) and d(yz) orbitals. Furthermore, the bare interpocket and intrapocket interactions within each subset are nearly equal. In this situation, small changes in the intrapocket and interpocket interactions due to renormalizations by high-energy fermions give rise to a variety of different gap structures. We focus on s-wave pairing which, as experiments show, is the most likely pairing symmetry in LiFeAs. We find four different configurations of the s-wave gap immediately below T-c: one in which the superconducting gap changes sign between two inner hole pockets and between the outer hole pocket and two electron pockets, one in which the gap changes sign between two electron pockets and three hole pockets, one in which the gap on the outer hole pocket differs in sign from the gaps on the other four pockets, and one in which the gaps on two inner hole pockets have one sign and the gaps on the outer hole pockets and on electron pockets have different sign. Different s-wave gap configurations emerge depending on whether the renormalized interactions increase attraction within each subset or increase the coupling between particular components of the two subsets. We discuss the phase diagram and experimental probes to determine the structure of the superconducting gap in LiFeAs. We argue that the state with opposite sign of the gaps on the two inner hole pockets has the best overlap with ARPES data. We also argue that at low T, the system may enter into a "mixed" s + is state, in which the phases of the gaps on different pockets differ by less than p and time-reversal symmetry is spontaneously broken.