耦合Majorana束缚态量子点系统的Andreev反射
发布时间：2019-06-05 07:56
【摘要】：近年来,由于Majorana费米子在基础理论和量子计算中的重要地位,在凝聚态材料中寻找Majorana束缚态(MBSs)已经成为研究热点.大量实验和理论研究指出借助量子点结构探测MBSs是一个很好的方法.量子点体系独特的输运性质及量子隧穿效应、量子干涉效应、Fano效应等现象为研究MBSs提供了良好平台.耦合量子点体系与单量子点相比,具有更多可调结构参数,因而具有重要的理论和实用价值.当量子点两端连接在正常金属电极和超导电极之间时,会产生Andreev反射.尤其能量处于超导子带隙之内时,电流几乎全部来源于Andreev反射,借此可以直接探测子带隙内的状态.本论文,主要研究MBSs耦合量子点体系,当它们连接正常金属和超导电极两端时该体系的输运性质,重点揭示MBSs对其Andreev反射的影响.我们首先研究正常金属电极和超导电极之间耦合MBSs单量子点的Andreev反射.研究发现,量子点与电极之间耦合强度合适时,MBSs对Andreev反射电导有增强的作用.适当调节量子点与MBS之间的耦合强度以及两个MBSs之间的耦合强度可以观察到Fano型Andreev反射电导曲线.当只有量子点与一个MBS耦合而忽略两个MBSs之间的耦合时,零费米能处的Andreev反射电导总为20 021/2()eG Gh?,体现明显的Majorana费米子特征.除此之外,我们还总结了产生共振Andreev反射的条件.我们对T型双量子点耦合MBSs的模型也进行了研究,并且将正常金属电极与超导电极连接在量子点两端,研究了能量处于超导带隙中的Andreev反射电导.结果发现,当只有一个量子点(量子点1)连接在电极两端时,零费米能附近出现共振峰,当量子点2与量子点1耦合时,由于量子相干效应,在能量等于量子点2能级处出现了Fano振荡.如果将MBS与量子点2耦合,Andreev反射电导曲线出现了新的特征.首先,在零费米能附近出现了一对新的Fano型振荡峰,并且引起原来Fano振荡峰的位置向两侧移动.其次,如果忽略两个MBSs之间的相互作用,零费米能点的Andreev反射电导为定值01/2G,与量子点能级、双量子点之间耦合强度以及量子点与MBS之间的耦合强度无关.这个结果与T型双量子点耦合一个普通费米子不同.我们希望这些研究结果有助于理解与MBSs相关的Andreev反射现象,并且期待能对MBSs在量子计算中的应用起到一定的参考价值.
[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，
本文编号：2493367
[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，
本文编号：2493367
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