硅烯异质结及纳米带的输运性质研究

Silicene consists of a honeycomb lattice of silicon atoms with bucked sublattices made of A sites and B sites. The states near the K and K’ points of the hexagonal Brillouin zone can be described by the Dirac theory as in graphene, the transport properties of which can be easily modulated by the external electric fields due to the bucked structure. The novelty phenomena in silicene systems have attracted much interest in recent years. .The goal of this project is to investigate the transport properties, such as Klein tunneling, valley-filtering effect and spin polarization in the silicene heterojunctions and nanoribbons according to their electronic structures. The content of the research project includes the following items: (1) We will study the effect of the hopping energies, potential configurations on the Klein tunneling in p-n type and p-n-p type silicene heterojunctions.(2) Analyzing the combined effect of the spin-orbit couplings and the electric field on the valley polarization and the valley-filtering effect, we can obtain the system’s parameters and conditions for effectively modulating the valley polarization, to explain some reported experimental behaviors and propose several novelty phenomena. (3) We will explore the effect of the edge types, width, the hopping terms and disorder of the silicene nanoribbons on the band structures and the transport behaviors, and investigate the dependence of transport property on the electric field. (4) We plan to investigate the dependence of the spin polarization, valley polarization, and the conductance on the amplitude and the direction of the magnetic field in the silicene heterojunctions and nanoribbons. .To investigate the electrical and magnetic responsible behaviors of silicene systems may find some new quantum effects and phenomena different from that of the normal two-dimensional electron gases. It indicates the possibility of devising a novel performance and tunable silicene devices on the basis of the investigation of the transport properties.

硅烯具有低翘曲度的蜂窝状结构，呈现狄拉克费米子特性且易受外场调控，这种新奇量子物态及其性质近年来广受关注。本项目拟研究硅烯异质结和纳米带的Klein隧穿、谷极化和自旋极化等输运问题，着重关注低翘曲度结构引发的调控特性。具体研究内容为：（1）研究p-n型、p-n-p型硅烯异质结中Klein隧穿与格点跃迁系数、电势构型的依赖关系；（2）分析自旋-轨道耦合参数和外电场，对谷极化率及谷阀效应的共同影响，给出有效调节谷极化率的硅烯异质结参数和外场条件；（3）研究硅烯纳米条带边缘形貌、宽度、格点跃迁系数、缺陷对体系能带结构、输运性质的影响，考虑电场的共同作用效果；（4）计算磁场作用下硅烯体系的能带结构，研究磁场强度和方向对硅烯薄膜、纳米条带自旋极化、谷极化及电导的具体影响。探索硅烯异质结和纳米带中的新量子效应，为从原理上设计一些结构新颖、性能优异和功能可调的电子器件奠定物理基础。

硅烯独特的，低翘曲度的蜂窝状结构，将谷自由度、自旋自由度耦合在一起，呈现丰富的谷极化效应，激发了物理学家极大的研究热情。本课题研究了硅烯异质结中应力调控的自旋和谷极化输运。我们发现，当只有应力作用时，不同能谷的透射曲线向相反方向偏移，自旋上和下的透射曲线重合。而当应力和外电场共同作用时，不同能谷和不同自旋的透射曲线均向相反方向偏移。因此，通过改变应力的大小和方向，可有效调控谷极化和自旋极化输运。应力诱导的谷和自旋偏移现象，可用来设计硅基谷电子学器件。研究了窄缩型硅烯纳米条带谷极化输运的外场调控作用。在中心散射区施加电势能，其子能带向上移动，从而与散射区外的能量不匹配，诱导了谷极化输运。当不存在电场和应力时，电势能和窄缩形结构产生了能带不匹配，使得电导呈现清晰的谷极化和零电导行为。外电场可打开能隙，导致额外的零电导。分析了石墨烯p-n-p、p-n结在外磁场作用下的Klein隧穿效应，发现磁场会破坏完美的Klein隧穿，并使角分辨透射率曲线向特定方向偏移。解析推导了透射曲线偏移垂直方向的对称轴，当磁场大于某个临界值时，无论势垒高度为多少，体系电导趋于零，实现了狄拉克费米子的磁场调控。拓展研究了包含自旋-轨道耦合相互作用的磷烯光跃迁现象。发现沿不同波矢方向，价带到导带的自旋翻转跃迁呈现显著的各向异性，而自旋守恒跃迁各向同性且基本不变。在圆偏光作用下，实验观察到二硫化钼中存在谷霍尔效应。谷霍尔信号存在相移且为周期函数，验证了自旋和谷间的强耦合效应。