First-principles study of the effective Hamiltonian for Dirac fermions with spin-orbit coupling in two-dimensional molecular conductor $\alpha$-(BETS)$_2$I$_3$
First-principles study of the effective Hamiltonian for Dirac fermions with spin-orbit coupling in two-dimensional molecular conductor $\alpha$-(BETS)$_2$I$_3$
复制标题
二维分子导体$alpha$-(BETS)$_2$I$_3$中自旋轨道耦合狄拉克费米子有效哈密顿量的第一性原理研究
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
Y. Suzumura
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作者：
T. Tsumuraya;Y. Suzumura
利用第一原理密度泛函理论（DFT）计算研究了准二维分子导体$\alpha$-(BETS)$_2$I$_3$ [= $\alpha$-(BEDT-TSeF)$_2$I$_3$]中与狄拉克电子相关的电子态。利用30K的低温结构，我们提供了一个紧密结合（TB）模型，该模型的分子间转移能由最大局域万尼尔函数（MLWFs）评估。分子固体的TB模型比较复杂；由于Se $p$轨道的离域特性，相关转移积分的数目相对较大。我们证明了具有无质量狄拉克色散的零隙态（ZGS）和具有约2 meV间接带隙的绝缘态两种情况的奇异行为。前一个模型参数是在无自旋轨道耦合（SOC）的情况下由标量相对论DFT计算得到的，后一个模型参数是在有自旋轨道耦合的情况下由全相对论计算得到的。通过将Dirac点附近的能谱与时间反转不变动量（TRIM）下的特征值进行比较，分析了Dirac点附近的能谱。利用自洽全相对论DFT计算中得到的Bloch函数生成的MLWFs，建立了一个精确的有效哈密顿量。我们还通过合理的拟合确定了给出与DFT波段对应的频谱的位电位。
We study the electronic states associated with Dirac electrons in quasi-two-dimensional molecular conductor $\alpha$-(BETS)$_2$I$_3$ [= $\alpha$-(BEDT-TSeF)$_2$I$_3$] using first-principles density-functional theory (DFT) calculations. Using a low-temperature structure of 30K, we provide a tight-binding (TB) model with intermolecular transfer energies evaluated from maximally-localized Wannier functions (MLWFs). The TB model for the molecular solid is complicated; the number of relevant transfer integral is relatively large due to the delocalized character of Se $p$ orbitals. We demonstrate exotic behaviors of both cases of a zero-gap state (ZGS) with massless Dirac dispersion and an insulating state with an indirect band gap of about 2 meV. The former model parameters are extracted from a scalar-relativistic DFT calculation in the absence of spin-orbit coupling (SOC), and those of the latter model are obtained from the full-relativistic calculation in the presence of SOC. The energy spectrum close to the Dirac point is analyzed by comparing it with some eigenvalues at the time-reversal invariant momentum (TRIM). A precise effective Hamiltonian is developed using MLWFs generated from Bloch functions obtained in self-consistent full-relativistic DFT calculations. We also determined site-potentials that give the spectrum corresponding to the DFT bands by a reasonable fitting.