$α$ -（BEDT-TTF）$_2$ I $_3$有机导体中Dirac点的存在与合并
Existence and merging of Dirac points in $α$-(BEDT-TTF)$_2$I$_3$ organic conductor
摘要：
本文重新研究了3/4填充$α$ -（BEDT-TTF）$_2$ I $_3$导电平面价带与导带之间Dirac点的存在性和稳定性条件。我们考虑通常最近的neigbhor紧束缚模型与七个转移能，取决于所施加的压力。由于布拉维晶格的每个晶胞有四个不同的分子（A，A '，B，C），因此对于布里渊区的每个波矢量$\mathbf{k}$，相应的布洛赫哈密顿量是$4\times4$矩阵${\cal H}({\bm k})$。在以前的工作中，狄拉克点的研究是通过直接数值对角化矩阵${\cal H}({\bm k})$。在这项工作中，我们开发了一种新的分析方法，允许分析狄拉克点的存在性和稳定性条件，从他们的合并性质的知识在时间反转点。在这种方法中，我们可以彻底讨论每个转移积分的作用，并证明反演对称性是方便的，但不是必要的。
英文摘要：
We reexamine the existence and stability conditions of Dirac points between valence and conduction bands of 3/4 filled $α$-(BEDT-TTF)$_2$I$_3$ conducting plane. We consider the usual nearest neigbhor tight binding model with the seven transfer energies that depend on the applied pressure. Owing to the four distinct molecules (A, A', B, C) per unit cell of the Bravais lattice, the corresponding Bloch Hamiltonian is a $4\times4$ matrix ${\cal H}({\bm k})$ for each wave vector $\mathbf{k}$ of the Brillouin zone. In most previous works the study of Dirac points was achieved through direct numerical diagonalization of matrix ${\cal H}({\bm k})$. In this work we develop a novel analytical approach which allows to analyze the existence and stability conditions of Dirac points from the knowledge of their merging properties at time reversal points. Within this approach we can discuss thoroughly the role of each transfer integrals and demonstrate that inversion symmetry is convenient but not necessary.
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