节线拓扑半金属拥有的电子结构

描述

 

01 引言

拓扑材料作为一类具有独特量子物态性质的特殊材料,其相关研究受到科研人员的广泛关注和重视。尤其是在拓扑绝缘体的理论预测被实验首次成功观测后,拓扑材料的相关研究迅速成为当前凝聚态物理和材料等领域的前沿热点方向。随着微纳加工技术的工艺进步和制造设备大量普及,以及材料计算领域高通量的应用,拓扑材料家族从较早的拓扑绝缘体逐步拓展到拓扑半金属体系。同拓扑绝缘体类似,拓扑半金属材料也存在受到对称性保护的能带反转情况,但与拓扑绝缘体最根本的区别在于,拓扑半金属的体态不是绝缘的而是金属性的,并且在费米能级附近的能带重叠区域呈现显著的线性交叉特性。本项目重点关注节线拓扑半金属,主要原因在于节线拓扑半金属拥有更为特殊的电子结构。主要体现在,节线拓扑半金属中能带交叉形成的不再是零维的节点,而是一维的节线(可以看做是由一系列连续的Dirac或者Weyl点构成)。由于其特殊的节线型能带交叉,节线拓扑半金属展现许多新奇的物理特征,包括鼓膜状的拓扑表面态,丰富的磁、电输运行为等。

02 成果简介

通过本项目的开展,基于第一性原理计算和材料结构搜索预测,成功预言了一系列正交结构Ti基双元半金属材料TiX2(X = S, Se 和 Te),尤其是其能带结构在费米能级附近展示出了一个拓扑节线环。对比以往报道的拓扑节线材料,该体系中的拓扑节线表现出了如下的优越特性:1)费米能带附近能带结构简单,只存在拓扑节线相关能带的交叉,其他部位存在很大的带隙;2)对应的拓扑节线正好分布在费米能级附近,对于后期实验观测难度要求较小;3)只存在一个拓扑节线环,没有其它额外拓扑元素,有利于节线环的相关属性研究。如此理想的拓扑特性,可以进一步激发相关实验和理论工作的开展。最后,由于该材料体系还未经过实验合成,我们通过计算研究了其稳定性,尤其是通过鸿之微的DS-PAW软件验证了其机械力学稳定性,并提供了相应的力学性能参数,可为后期实验合成和应用提供一定指导。

03 图文导读

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Figure 1 The crystal structure for TiS2 material and its corresponding Brillouin zone with high symmetry points and paths. The translucent blue color shaded area indicates the ky = 0 plane projection.

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Figure 2: The calculated phonon dispersion spectrum in the left panel and directional dependent mechanical properties in the right panel for TiS2 material.

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Figure 3: The calculated electronic band structures near the Fermi energy level for TiS2 material. Two band crossing points around Fermi energy level are indicated by the blue arrows. The element contribution is projected by the color weight.

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Figure 4: The calculated band dispersions for TiS2 material in the ky = 0 plane in the left panel. Note that only the two intersecting bands are shown and their crossing forms a ring, as highlighted by the red color dot. The high symmetry points are marked on the bottom rectangle of ky = 0 plane, where several path segments are shown. In the left panel, band structures along these path segments are displayed and the maximum energy variation for the crossing points is derived as 0.04 eV.

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Figure 5: The band structure comparison a) for TiS2 material along Z‒Γ‒X path between the DFT calculation and Wannier function fitting without SOC effect. The corresponding surface band structure projection in ky = 0 plane for Ti-termination b) and S-termination c)。 The drumhead surface states are denoted by arrows.

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Figure 6: The band structure comparison a) for TiS2 material along Z‒Γ‒X path between the DFT calculation and Wannier function fitting with SOC effect. The induced gap values are indicated in the figure. The corresponding surface band structure projection in ky = 0 plane for Ti-termination b) and S-termination c)。 The drumhead surface states are denoted by arrows.

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Figure 7: The stack plot of constant energy contours without SOC effect a) and with SOC effect b) for the surface band structure projection of TiS2 material in ky = 0 plane with Ti-termination. The evolution of the drumhead surface states at different energy slices are indicated by the arrows.

04 小结

本工作组基于第一性原理计算和材料结构搜索预测,预言了一系列正交结构Ti基双元半金属材料TiX2(X = S, Se 和 Te),其能带结构在费米能级附近展示出性质十分理想的拓扑节线环。通过计算研究了其稳定性,尤其是通过DS-PAW软件验证了其机械力学稳定性,并提供了相应的力学性能参数,可为后期实验合成和应用提供一定指导。

 

原文标题:文献赏析|节线型拓扑半金属理论预测和研究

文章出处:【微信公众号:鸿之微】欢迎添加关注!文章转载请注明出处。  

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