低维材料中的拓扑电子态以及电子自旋极化的理论研究

发布时间：2018-03-19 14:46

  本文选题：自旋轨道耦合　切入点：拓扑特性　出处：《山东大学》2016年博士论文　论文类型：学位论文

【摘要】：伴随着自旋电子学的迅猛发展,自旋轨道耦合效应逐步引起人们的广泛关注。自旋轨道耦合效应可以诱导产生很多新颖的物理现象,如自旋霍尔效应等,并在自旋场效应晶体管以及自旋量子计算机等方面具有重要的应用。无需外磁场以及磁性材料,自旋轨道耦合效应呈现出了一种全电学的方案来控制自旋,为设计新型电子器件奠定了理论基础。作为一种全新的物质形态,基于自旋轨道耦合效应的拓扑绝缘体受到越来越多的关注,研究领域横跨凝聚态物理,固态化学,材料科学等多门学科。自旋轨道耦合作用下,由于受到拓扑保护,拓扑绝缘体边界或表面总是存在导电的边缘态。拓扑绝缘体材料与量子自旋霍尔效应和量子反常霍尔效应紧密相连,在自旋电子学器件方面有广泛的应用前景。在纳米材料中引入电子自旋极化也是自旋电子学领域的一个重要的研究热点。与无机材料相比,有机纳米材料不仅仅合成简单,易于大面积处理。更重要是,基于有机纳米材料的自旋电子学器件柔韧性较好,机械性能优良,拥有较为丰富的电磁光特性。此外,基于电子自旋的纳米器件能够大大提高信息处理速度和存储密度,而且具有非易失性,低能耗等优点。因此为了满足特定的自旋电子学器件性能需求,调控有机纳米材料的电子自旋极化变得尤其重要。本论文以铋化镓,碳氮类石墨烯,氮化硼等二维材料为研究对象,采用量子力学的第一性原理计算方法,对材料中与自旋轨道耦合相关的拓扑电子态和基于p轨道的电子自旋极化进行了系统的模拟研究。主要研究结果包括以下几个方面：(a)从理论上证明：类金刚石结构的氢化的铋化镓双层(2DCD GaBiH)是一种结构稳定的二维拓扑绝缘体,在上述材料的纳米带边缘上存在零能隙的手性边缘态,其拓扑非平凡的能带主要来源于内部sp3杂化的原子。伴随着px,y能带的反转,其拓扑非平凡带隙可高达0.320eV,表明该材料有望实现室温量子自旋霍尔效应。(b)对实验上已经合成的碳氮类石墨烯(g-C6N6)的电子结构进行了理论研究,证明该材料具有拓扑非平凡的电子态。其拓扑非平凡的电子态主要来源于氮原子的Px,y轨道,符合Ruby模型。其中的自旋轨道耦合强度高于石墨烯和硅烯,在K点和r点分别打开了5.50meV及8.27meV的带隙,可以在低于95K的温度下实现量子自旋霍尔效应。(c)系统的研究了具有分形结构的碳氮类石墨烯(C4N3-H)的电子自旋极化和磁有序,证明随着分形阶数的增高,材料的电子自旋极化和铁磁性逐渐增强。电子自旋极化主要来源于碳原子和氮原子的pz轨道,近似服从Lieb定理。蒙特卡洛模拟的结果显示,其居里温度远高于室温(TC-1105K),具有稳定的室温铁磁基性。这类具有分形结构的碳氮类石墨烯材料在自旋电子器件中具有潜在的应用价值,同时为涉及新型的d0有机磁性材料提供了有益的参考。(d)系统的研究了由石墨烯和氮化硼组成的异质结构的电子结构,发现三角形的石墨烯量子点具有自旋极化的基态。电子结构在费米能级附近拥有自旋极化的零能态(ZESs),该零能态的数目与石墨烯量子点的几何结构以及BCN的原子比例有关,与氮化硼量子点几何结构无关。体系的净自旋(S)符合Lieb定理：S=|NA-NB|/2,NA和NB为石墨烯量子点中两套子格的原子数目。此外,BN/Graphene异质材料中电子的自旋极化可以采用平均场近似下的π电子的Hubbard模型来描述。上述结果为研究BCN材料中磁性的起源,以及新型非金属磁性材料提供了理论依据。(e)从理论上预言,氟化可以在六方氮化硼中引起电子的自旋极化和磁有序。电子自旋极化主要来源于氟化的硼原子周围的氮原子。局域磁矩之间通过直接交换机制产生铁磁序。此外,硼空位缺陷也会诱发产生电子的自旋极化,并与氟原子吸附缺陷之间形成稳定的铁磁耦合。我们和实验课题组合作,利用氟化铵来辅助剥离六方氮化硼和固态反应的方法,制备了包含氟原子吸附缺陷和空位缺陷的氮化硼纳米片,并成功地观测到了室温铁磁性,验证了理论预言,为合成磁性氮化硼纳米材料打下了理论和实验基础。
[Abstract]:With the rapid development of spintronics, spin orbit coupling effect has gradually attracted people's attention. The effect of spin orbit coupling can induce many novel physical phenomena, such as spin Holzer effect, and calculate the spin field effect transistor, spin quantum machines have important applications. Without external magnetic field and magnetic materials. The effect of spin orbit coupling shows a full electrical scheme to control the spin, which laid a theoretical foundation for the design of new electronic devices. As a new form of matter, topological insulator spin orbit coupling effect has attracted more and more attention on research across the field of condensed matter physics, solid state chemistry, material science disciplines. Spin orbit coupling, due to topological topological insulator boundary or surface protection, there is always the edge of state electricity. The vast topology Edge materials and quantum spin quantum anomalous Holzer effect and Holzer effect are closely linked, and has wide application prospect in spintronics devices. One of the important research into electron spin polarization and spin electronics in the field of nano materials. Compared with inorganic materials, organic synthesis of nano materials not only simple, suitable for large area processing more important is, spintronics devices of organic materials based on good flexibility, excellent mechanical properties, optical properties have electromagnetic abundant. In addition, nano spin electronic devices can greatly improve the speed of information processing and storage based on density, but also has a non-volatile, low power consumption and so on. Therefore, in order to meet the needs of spintronics device specific performance requirements, the regulation of electron spin polarization in organic nano materials has become particularly important. In this paper, bismuth gallium, graphite like carbon and nitrogen Graphene, boron nitride and other two-dimensional materials as the research object, first principle calculation method based on topological quantum mechanics, electronic states and spin orbit coupling materials and electron spin polarization of the P orbit based on simulated system. The main research results are as follows: (a) theoretically prove: hydrogenated diamond-like structure of bismuth gallium arsenide (2DCD GaBiH) is a double 2D topological insulator a stable structure, in the nano material with a chiral edge states zero energy gap on the edge of the topological non trivial band is due to the internal SP3 hybrid atoms. With Px, y with the reverse, the topological non trivial band gap can be as high as 0.320eV, shows that the material is expected to achieve room temperature quantum spin Holzer (b). The effect of carbon and nitrogen on the experimental class of graphene (g-C6N6) has been synthesized in electronic structure theory research, The material has a non trivial topological electronic states. The non trivial topology electronic states mainly originates from the nitrogen atom Px, y track, with the Ruby model. The spin orbit coupling which is higher than that of graphene and graphene on silicon, K and R respectively opened the band gap of 5.50meV and 8.27meV, can be achieved the spin quantum Holzer effect at a temperature lower than 95K. (c) carbon nitrogen graphene has the fractal structure of the system (C4N3-H) of the electron spin polarization and magnetic ordering, that with the increase of fractal order, the material of the electron spin polarization and magnetic iron gradually increased. Mainly from the electron spin polarization carbon and nitrogen atoms of the PZ orbital, approximately obeys the Lieb theorem. The Monte Carlo simulation results show that the Curie temperature is much higher than that at room temperature (TC-1105K), with a stable room temperature ferromagnetic medium. This kind of fractal structure of graphene materials in carbon and nitrogen 鑷�鏃嬬數瀛愬櫒浠朵腑鍏锋湁娼滃湪鐨勫簲鐢ㄤ环澹�

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