低維材料中的拓?fù)潆娮討B(tài)以及電子自旋極化的理論研究
發(fā)布時(shí)間：2018-03-19 14:46
本文選題：自旋軌道耦合 切入點(diǎn)：拓?fù)涮匦?/strong> 出處：《山東大學(xué)》2016年博士論文 論文類型：學(xué)位論文
【摘要】：伴隨著自旋電子學(xué)的迅猛發(fā)展,自旋軌道耦合效應(yīng)逐步引起人們的廣泛關(guān)注。自旋軌道耦合效應(yīng)可以誘導(dǎo)產(chǎn)生很多新穎的物理現(xiàn)象,如自旋霍爾效應(yīng)等,并在自旋場效應(yīng)晶體管以及自旋量子計(jì)算機(jī)等方面具有重要的應(yīng)用。無需外磁場以及磁性材料,自旋軌道耦合效應(yīng)呈現(xiàn)出了一種全電學(xué)的方案來控制自旋,為設(shè)計(jì)新型電子器件奠定了理論基礎(chǔ)。作為一種全新的物質(zhì)形態(tài),基于自旋軌道耦合效應(yīng)的拓?fù)浣^緣體受到越來越多的關(guān)注,研究領(lǐng)域橫跨凝聚態(tài)物理,固態(tài)化學(xué),材料科學(xué)等多門學(xué)科。自旋軌道耦合作用下,由于受到拓?fù)浔Ｗo(hù),拓?fù)浣^緣體邊界或表面總是存在導(dǎo)電的邊緣態(tài)。拓?fù)浣^緣體材料與量子自旋霍爾效應(yīng)和量子反�；魻栃�(yīng)緊密相連,在自旋電子學(xué)器件方面有廣泛的應(yīng)用前景。在納米材料中引入電子自旋極化也是自旋電子學(xué)領(lǐng)域的一個(gè)重要的研究熱點(diǎn)。與無機(jī)材料相比,有機(jī)納米材料不僅僅合成簡單,易于大面積處理。更重要是,基于有機(jī)納米材料的自旋電子學(xué)器件柔韌性較好,機(jī)械性能優(yōu)良,擁有較為豐富的電磁光特性。此外,基于電子自旋的納米器件能夠大大提高信息處理速度和存儲(chǔ)密度,而且具有非易失性,低能耗等優(yōu)點(diǎn)。因此為了滿足特定的自旋電子學(xué)器件性能需求,調(diào)控有機(jī)納米材料的電子自旋極化變得尤其重要。本論文以鉍化鎵,碳氮類石墨烯,氮化硼等二維材料為研究對象,采用量子力學(xué)的第一性原理計(jì)算方法,對材料中與自旋軌道耦合相關(guān)的拓?fù)潆娮討B(tài)和基于p軌道的電子自旋極化進(jìn)行了系統(tǒng)的模擬研究。主要研究結(jié)果包括以下幾個(gè)方面：(a)從理論上證明：類金剛石結(jié)構(gòu)的氫化的鉍化鎵雙層(2DCD GaBiH)是一種結(jié)構(gòu)穩(wěn)定的二維拓?fù)浣^緣體,在上述材料的納米帶邊緣上存在零能隙的手性邊緣態(tài),其拓?fù)浞瞧椒驳哪軒е饕獊碓从趦?nèi)部sp3雜化的原子。伴隨著px,y能帶的反轉(zhuǎn),其拓?fù)浞瞧椒矌犊筛哌_(dá)0.320eV,表明該材料有望實(shí)現(xiàn)室溫量子自旋霍爾效應(yīng)。(b)對實(shí)驗(yàn)上已經(jīng)合成的碳氮類石墨烯(g-C6N6)的電子結(jié)構(gòu)進(jìn)行了理論研究,證明該材料具有拓?fù)浞瞧椒驳碾娮討B(tài)。其拓?fù)浞瞧椒驳碾娮討B(tài)主要來源于氮原子的Px,y軌道,符合Ruby模型。其中的自旋軌道耦合強(qiáng)度高于石墨烯和硅烯,在K點(diǎn)和r點(diǎn)分別打開了5.50meV及8.27meV的帶隙,可以在低于95K的溫度下實(shí)現(xiàn)量子自旋霍爾效應(yīng)。(c)系統(tǒng)的研究了具有分形結(jié)構(gòu)的碳氮類石墨烯(C4N3-H)的電子自旋極化和磁有序,證明隨著分形階數(shù)的增高,材料的電子自旋極化和鐵磁性逐漸增強(qiáng)。電子自旋極化主要來源于碳原子和氮原子的pz軌道,近似服從Lieb定理。蒙特卡洛模擬的結(jié)果顯示,其居里溫度遠(yuǎn)高于室溫(TC-1105K),具有穩(wěn)定的室溫鐵磁基性。這類具有分形結(jié)構(gòu)的碳氮類石墨烯材料在自旋電子器件中具有潛在的應(yīng)用價(jià)值,同時(shí)為涉及新型的d0有機(jī)磁性材料提供了有益的參考。(d)系統(tǒng)的研究了由石墨烯和氮化硼組成的異質(zhì)結(jié)構(gòu)的電子結(jié)構(gòu),發(fā)現(xiàn)三角形的石墨烯量子點(diǎn)具有自旋極化的基態(tài)。電子結(jié)構(gòu)在費(fèi)米能級附近擁有自旋極化的零能態(tài)(ZESs),該零能態(tài)的數(shù)目與石墨烯量子點(diǎn)的幾何結(jié)構(gòu)以及BCN的原子比例有關(guān),與氮化硼量子點(diǎn)幾何結(jié)構(gòu)無關(guān)。體系的凈自旋(S)符合Lieb定理：S=|NA-NB|/2,NA和NB為石墨烯量子點(diǎn)中兩套子格的原子數(shù)目。此外,BN/Graphene異質(zhì)材料中電子的自旋極化可以采用平均場近似下的π電子的Hubbard模型來描述。上述結(jié)果為研究BCN材料中磁性的起源,以及新型非金屬磁性材料提供了理論依據(jù)。(e)從理論上預(yù)言,氟化可以在六方氮化硼中引起電子的自旋極化和磁有序。電子自旋極化主要來源于氟化的硼原子周圍的氮原子。局域磁矩之間通過直接交換機(jī)制產(chǎn)生鐵磁序。此外,硼空位缺陷也會(huì)誘發(fā)產(chǎn)生電子的自旋極化,并與氟原子吸附缺陷之間形成穩(wěn)定的鐵磁耦合。我們和實(shí)驗(yàn)課題組合作,利用氟化銨來輔助剝離六方氮化硼和固態(tài)反應(yīng)的方法,制備了包含氟原子吸附缺陷和空位缺陷的氮化硼納米片,并成功地觀測到了室溫鐵磁性,驗(yàn)證了理論預(yù)言,為合成磁性氮化硼納米材料打下了理論和實(shí)驗(yàn)基礎(chǔ)。
[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 鑷棆鐢?shù)瀛愬櫒錃g涓叿鏈夋綔鍦ㄧ殑搴旂敤浠峰，
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