【摘要】：近年來,由于Majorana費(fèi)米子在基礎(chǔ)理論和量子計算中的重要地位,在凝聚態(tài)材料中尋找Majorana束縛態(tài)(MBSs)已經(jīng)成為研究熱點(diǎn).大量實驗和理論研究指出借助量子點(diǎn)結(jié)構(gòu)探測MBSs是一個很好的方法.量子點(diǎn)體系獨(dú)特的輸運(yùn)性質(zhì)及量子隧穿效應(yīng)、量子干涉效應(yīng)、Fano效應(yīng)等現(xiàn)象為研究MBSs提供了良好平臺.耦合量子點(diǎn)體系與單量子點(diǎn)相比,具有更多可調(diào)結(jié)構(gòu)參數(shù),因而具有重要的理論和實用價值.當(dāng)量子點(diǎn)兩端連接在正常金屬電極和超導(dǎo)電極之間時,會產(chǎn)生Andreev反射.尤其能量處于超導(dǎo)子帶隙之內(nèi)時,電流幾乎全部來源于Andreev反射,借此可以直接探測子帶隙內(nèi)的狀態(tài).本論文,主要研究MBSs耦合量子點(diǎn)體系,當(dāng)它們連接正常金屬和超導(dǎo)電極兩端時該體系的輸運(yùn)性質(zhì),重點(diǎn)揭示MBSs對其Andreev反射的影響.我們首先研究正常金屬電極和超導(dǎo)電極之間耦合MBSs單量子點(diǎn)的Andreev反射.研究發(fā)現(xiàn),量子點(diǎn)與電極之間耦合強(qiáng)度合適時,MBSs對Andreev反射電導(dǎo)有增強(qiáng)的作用.適當(dāng)調(diào)節(jié)量子點(diǎn)與MBS之間的耦合強(qiáng)度以及兩個MBSs之間的耦合強(qiáng)度可以觀察到Fano型Andreev反射電導(dǎo)曲線.當(dāng)只有量子點(diǎn)與一個MBS耦合而忽略兩個MBSs之間的耦合時,零費(fèi)米能處的Andreev反射電導(dǎo)總為20 021/2()eG Gh?,體現(xiàn)明顯的Majorana費(fèi)米子特征.除此之外,我們還總結(jié)了產(chǎn)生共振Andreev反射的條件.我們對T型雙量子點(diǎn)耦合MBSs的模型也進(jìn)行了研究,并且將正常金屬電極與超導(dǎo)電極連接在量子點(diǎn)兩端,研究了能量處于超導(dǎo)帶隙中的Andreev反射電導(dǎo).結(jié)果發(fā)現(xiàn),當(dāng)只有一個量子點(diǎn)(量子點(diǎn)1)連接在電極兩端時,零費(fèi)米能附近出現(xiàn)共振峰,當(dāng)量子點(diǎn)2與量子點(diǎn)1耦合時,由于量子相干效應(yīng),在能量等于量子點(diǎn)2能級處出現(xiàn)了Fano振蕩.如果將MBS與量子點(diǎn)2耦合,Andreev反射電導(dǎo)曲線出現(xiàn)了新的特征.首先,在零費(fèi)米能附近出現(xiàn)了一對新的Fano型振蕩峰,并且引起原來Fano振蕩峰的位置向兩側(cè)移動.其次,如果忽略兩個MBSs之間的相互作用,零費(fèi)米能點(diǎn)的Andreev反射電導(dǎo)為定值01/2G,與量子點(diǎn)能級、雙量子點(diǎn)之間耦合強(qiáng)度以及量子點(diǎn)與MBS之間的耦合強(qiáng)度無關(guān).這個結(jié)果與T型雙量子點(diǎn)耦合一個普通費(fèi)米子不同.我們希望這些研究結(jié)果有助于理解與MBSs相關(guān)的Andreev反射現(xiàn)象,并且期待能對MBSs在量子計算中的應(yīng)用起到一定的參考價值.
[Abstract]:In recent years, due to the important position of Majorana fermions in basic theory and quantum computing, the search for Majorana bound state (MBSs) in condensed matter materials has become a hot research topic. A large number of experiments and theoretical studies show that it is a good method to detect MBSs with the help of quantum dot structure. The unique transport properties, quantum tunneling effect, quantum interference effect and Fano effect of quantum dot system provide a good platform for the study of MBSs. Compared with single quantum dots, the coupled quantum dots system has more adjustable structural parameters, so it has important theoretical and practical value. When the two ends of the quantum dots are connected between the normal metal electrode and the superconducting electrode, Andreev reflection will be produced. Especially when the energy is in the superconducting band gap, almost all of the current comes from Andreev reflection, which can directly detect the state in the subband gap. In this thesis, the MBSs coupled quantum dot system is studied. When they connect the normal metal and the superconducting electrode, the transport properties of the system are studied, and the effect of MBSs on its Andreev reflection is revealed. We first study the Andreev reflection of MBSs single quantum dots coupled between normal metal electrodes and superconducting electrodes. It is found that MBSs can enhance the reflective conductivity of Andreev when the coupling strength between QDs and electrodes is suitable. The reflection conductivity curve of Andreev can be observed by properly adjusting the coupling strength between quantum dots and MBS and the coupling strength between two MBSs. When only quantum dots are coupled with one MBS and the coupling between two MBSs is ignored, the Andreev reflection conductivity at zero fermion is always 2021 鈮，

本文編號：2493367