本文選題：T-DQD系統(tǒng) + 電子關(guān)聯(lián)　； 參考：《四川師范大學(xué)》2015年碩士論文

【摘要】：隨著納米制備技術(shù)的發(fā)展和信息技術(shù)的需求,人們迫切希望研制出尺寸小、可靠性高的高度集成化量子器件,然而尺寸的減小將帶來(lái)一系列的邊界效應(yīng)問(wèn)題和量子效應(yīng)問(wèn)題。因此,為了研制出按量子力學(xué)原理工作的電子器件,人們把量子點(diǎn)系統(tǒng)的kondo效應(yīng)及其對(duì)介觀系統(tǒng)輸運(yùn)性質(zhì)的影響作為凝聚態(tài)物理中最重要的課題之一。目前,人們做了大量的工作去研究與鐵磁電極相連的T-DQD系統(tǒng),其特殊的不對(duì)等結(jié)構(gòu)顯示出一些有趣的現(xiàn)象:電子可分別通過(guò)中心量子點(diǎn)和邊耦合量子點(diǎn),因此我們可以把該模型作為理想的雙雜質(zhì)系統(tǒng)去研究強(qiáng)關(guān)聯(lián)效應(yīng)。前人的研究只涉及了量子點(diǎn)內(nèi)(忽略了點(diǎn)間)的庫(kù)侖排斥作用對(duì)電子輸運(yùn)的影響和電子的自旋極化運(yùn)輸,因此我們有必要去研究量子點(diǎn)間的庫(kù)侖作用、耦合強(qiáng)度等關(guān)聯(lián)效應(yīng)對(duì)電子態(tài)密度的影響。本文通過(guò)雙雜質(zhì)Anderson模型的哈密頓,利用隸玻色平均場(chǎng)技巧和運(yùn)動(dòng)方程方法求解了哈密頓,進(jìn)而得出了量子點(diǎn)中電子的態(tài)密度和透射幾率。通過(guò)比較不同參數(shù)下的圖像,來(lái)討論庫(kù)侖排斥作用等關(guān)聯(lián)效應(yīng)對(duì)kondo效應(yīng)的影響。研究結(jié)果表明:(1)庫(kù)侖排斥作用U極大地影響了電子的態(tài)密度。在對(duì)稱情況下,隨U的增大,kondo共振峰的寬度變窄了,說(shuō)明庫(kù)侖排斥作用壓制了kondo共振。這是因?yàn)樵谳^大的庫(kù)侖相互作用下,電子的雙占據(jù)情況被破壞了,從而阻礙了電子的隧穿,這是間接庫(kù)侖阻塞。而在非對(duì)稱情況下,當(dāng)U1.5時(shí),態(tài)密度的峰寬隨U的增大發(fā)生明顯的變窄,之后隨著U的繼續(xù)增大,共振峰的峰寬竟然變寬了,這是一種特殊的變化。(2)當(dāng)點(diǎn)間庫(kù)侖作用U?0時(shí),kondo共振峰的寬度隨邊耦合量子點(diǎn)的能級(jí)20E的增加變窄了,說(shuō)明邊耦合量子點(diǎn)的能級(jí)壓制了kondo共振。而在U?1.5的情況下,當(dāng)20E?2.0時(shí)共振峰的寬度隨20E的增加變窄了,之后隨著20E的繼續(xù)增大卻變寬了,這也是一種特殊的變化。(3)量子點(diǎn)間的耦合強(qiáng)度abt在弱耦合區(qū)時(shí)對(duì)kondo效應(yīng)的影響不大,進(jìn)入到強(qiáng)耦合區(qū)后對(duì)kondo共振有較大的影響,表現(xiàn)為kondo共振峰的寬度隨abt的增大變窄了,壓制了kondo共振。(4)偏壓e V使kondo共振峰的峰值位置發(fā)生了偏移,并且使kondo共振峰的寬度發(fā)生了明顯的變化。由于T型雙量子點(diǎn)結(jié)構(gòu)是一個(gè)可以包含單個(gè)和雙個(gè)量子點(diǎn)的良好系統(tǒng),所以我們有理由相信這些性質(zhì)對(duì)T型雙量子點(diǎn)系統(tǒng)在理論及應(yīng)用方面的研究有著積極的指導(dǎo)意義。
[Abstract]:With the development of nanocrystalline preparation technology and the demand of information technology, people are eager to develop highly integrated quantum devices with small size and high reliability. However, a series of boundary effect and quantum effect problems will be caused by the reduction of size. Therefore, in order to develop electronic devices based on the principle of quantum mechanics, the kondo effect of quantum dot system and its influence on the transport properties of mesoscopic system are considered as one of the most important topics in condensed matter physics. At present, a great deal of work has been done to study the T-DQD system connected with ferromagnetic electrodes. Its special unequal structure shows some interesting phenomena: electrons can pass through central quantum dots and edge-coupled quantum dots, respectively. Therefore, we can study the strong correlation effect by using this model as an ideal double impurity system. Previous studies only deal with the effect of Coulomb repulsion on electron transport and electron spin polarization transport in quantum dots, so it is necessary to study the Coulomb interaction between quantum dots. The effect of coupling intensity and other correlation effects on the electron density of states. In this paper, the Hamiltonian of the Anderson model with double impurity is solved by using the Libose mean field technique and the equation of motion method, and the density of state and the transmission probability of the electron in the quantum dot are obtained. The effects of Coulomb exclusion and other correlation effects on the kondo effect are discussed by comparing the images with different parameters. The results show that the Coulomb repulsion U greatly affects the density of states of electrons. Under symmetric conditions, the width of kondo resonance peak becomes narrower with the increase of U, which indicates that the Coulomb repulsion suppresses the kondo resonance. This is because the double occupation of electrons is destroyed under the larger Coulomb interaction, which hinders the tunneling of electrons, which is an indirect Coulomb blocking. Under asymmetric condition, the peak width of the density of states shrinks obviously with the increase of U when U 1.5, and then with the increase of U, the width of the resonance peak becomes wider. This is a special variation. (2) when the interdot Coulomb interaction is U0, the width of the kondo resonance peak becomes narrower with the increase of the energy level 20E of the edge-coupled quantum dot, which indicates that the energy level of the edge-coupled quantum dot suppresses the kondo resonance. However, the width of the resonance peak becomes narrower with the increase of 20E and then widens with the further increase of 20E at U1. 5. This is also a special variation. The coupling intensity abt between quantum dots has little effect on the kondo effect in the weakly coupled region, but it has a great influence on the kondo resonance after entering the strong coupling region, which shows that the width of the kondo resonance peak becomes narrower with the increase of abt. Suppression of kondo resonance. 4) bias voltage EV shifts the peak position of kondo resonance peak and makes the width of kondo resonance peak change obviously. Since the structure of T-type double quantum dots is a good system which can contain single and double quantum dots, we have reason to believe that these properties have a positive guiding significance in the theoretical and practical research of T-type double quantum dot systems.
【學(xué)位授予單位】：四川師范大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：O471.1

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本文編號(hào)：1823089