Andreev Reflection Properties In Quantum Dots And Majorana Bound States Coupled System

In recent years,the preparation technology of Majorana bound states(MBSs)has been found.Because of its large potential in quantum computing,the researches of transport properties in quantum dot system which droved by Majorana bound states has been a hot topic in mesoscopic physics.In the view of basic research,it is necessary and meaningful to study the transport properties in the system which coupled with Majorana bound states.In this thesis,we mainly focus on the Andreev reflection properties in quantum dots system coupled with Majorana bound states.In such a system,with the help of the non-equilibrium Green function method,we calculate the conductance both theoretical and numerical sides.Firstly,we investigate the Andreev reflection in a parallel mesoscopic circuit with Majorana bound states.It is found that in such a structure,the Andreev conductance can be manipulated in a highly efficient way,by the adjustment of bias voltage,dot levels,inter-MBS coupling,and the applied magnetic flux.Besides,the dot-MBS coupling manner is an important factor to modulate the Andreev current,because it influences the period of the conductance oscillation.In the Nambu representation,by discussing the underlying quantum interference mechanism,the Andreev-reflection property can be explained in detail.Secondly,we investigate the Andreev reflection on the interface between normal and superconducting leads that modified by the Majorana doublet.It is found that the Andreev reflection properties can be manipulated when Majorana doublet is existed in the superconductor.We calculate the exact location of the conductance peaks and find that the calculated values of the conductance peaks are equal to the numerical results.In addition,when the quantum dot energy level is far away from the Fermi level,the conductance of the system is suppressed.With the increase of the quantum dot's level,d?,the suppression effect of the conductance peaks will become more obviously.We believe that all the results can assist to understand the nontrivial role of theMajorana bound states or Majorana doublet in driving the Andreev reflection.