有机导体$α$ -（BEDT-TTF）$_2$ I $_3$电荷有序态中Dirac电子对的出现
Emergence of Dirac Electron Pair in Charge Ordered State of Organic Conductor $α$-(BEDT-TTF)$_2$I$_3$
摘要：
利用Hartree平均场理论中的扩展哈伯德模型，重新研究了$α$ -（BEDT-TTF）$_2$ I $_3$在压力作用下条形电荷有序态的能带结构.通过增加压力，我们发现从一个传统的绝缘体的拓扑过渡与一个单一的最小值的色散关系在M点的布里渊区，朝着一个新的阶段，表现出双最小值。这种跃迁的特征是出现了一对质量有限的狄拉克电子。使用Luttinger-Kohn表示在M点，它表明，这种变化的能带结构可以描述一个有效的$2 \times 2$低能量哈密顿与一个单一的驱动参数。通过计算Berry曲率，证实了该相变的拓扑性质。Berry曲率在常规相为零，而在新相为符号相反的双峰结构。我们比较这种过渡的结构与一个简单的情况下，发生在两个组件系统，如氮化硼。
英文摘要：
We re-examine the band structure of the stripe charge ordered state of $α$-(BEDT-TTF)$_2$I$_3$ under pressure by using an extended Hubbard model within the Hartree mean-field theory. By increasing pressure, we find a topological transition from a conventional insulator with a single-minimum in the dispersion relation at the M-point in the Brillouin zone, towards a new phase which exhibits a double-minimum. This transition is characterized by the appearance of a pair of Dirac electrons with a finite mass. Using the Luttinger-Kohn representation at the M-point, it is shown that such a variation of the band structure can be described by an effective $2 \times 2$ low energy Hamiltonian with a single driving parameter. The topological nature of this transition is confirmed by the calculation of the Berry curvature which vanishes in the conventional phase and has a double peak structure with opposite signs in the new phase. We compare the structure of this transition with a simpler situation which occurs in two-component systems, like boron-nitride.
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