Center for Frontier Science, Chiba University, Chiba 263-8522, Japan.
Department of Physics, Technical University Dresden, 01069 Dresden, Germany.
Phys Rev Lett. 2018 Jun 15;120(24):247602. doi: 10.1103/PhysRevLett.120.247602.
We analyze the measured optical conductivity spectra using the density-functional-theory-based electronic structure calculation and density-matrix renormalization group calculation of an effective model. We show that, in contrast to a conventional description, the Bose-Einstein condensation of preformed excitons occurs in Ta_{2}NiSe_{5}, despite the fact that a noninteracting band structure is a band-overlap semimetal rather than a small band-gap semiconductor. The system above the transition temperature is therefore not a semimetal but rather a state of preformed excitons with a finite band gap. A novel insulator state caused by the strong electron-hole attraction is thus established in a real material.
我们使用基于密度泛函理论的电子结构计算和有效模型的密度矩阵重整化群计算来分析测量的光学电导率谱。我们表明，与传统描述相反，在 Ta_{2}NiSe_{5}中发生了玻色-爱因斯坦凝聚的预形成激子，尽管非相互作用的能带结构是带重叠的半金属，而不是小带隙半导体。因此，在相变温度以上的系统不是半金属，而是具有有限带隙的预形成激子的状态。因此，在真实材料中建立了一种由强电子-空穴吸引引起的新型绝缘态。
