Spin effects on transport and zero-bias anomaly in a hybrid Majorana wire-quantum dot system

Abstract

We examine the impact of spin effects on the nonequilibrium transport properties of a nanowire hosting Majorana zero-energy modes at its ends, coupled to a quantum dot junction with ferromagnetic leads. Using the real-time diagrammatic technique, we determine the current, differential conductance and current cross-correlations in the nonlinear response regime. We also explore transport in different magnetic configurations of the system, which can be quantified by the tunnel magnetoresistance. We show that the presence of Majorana quasiparticles gives rise to unique features in all spin-resolved transport characteristics, in particular, to zero-bias anomaly, negative differential conductance, negative tunnel magnetoresistance, and it is also reflected in the current cross-correlations. Moreover, we study the dependence of the zero-bias anomaly on various system parameters and demonstrate its dependence on the magnetic configuration of the system as well as on the degree of spin polarization in the leads. A highly nontrivial behavior is also found for the tunnel magnetoresistance, which exhibits regions of enhanced or negative values—new features resulting from the coupling to Majorana wire.

Cross-correlations between currents and tunnel magnetoresistance in interacting double quantum dot-Majorana wire system

“…For , the current does not flow through the system, however, the differential conductance clearly reveals a strong zero-bias peak associated with the Majorana modes leaking into the quantum dots. We note that the basic dependencies of the zero-bias anomaly on various model parameters have recently been studied in a hybrid Majorana system with one quantum dot coupled to ferromagnetic leads 53 . However, in the case of the double quantum dot-Majorana device considered here, we have the opportunity to study the behavior of a non-local zero-bias anomaly revealed in magnetotransport properties, which will be comprehensively discussed later on.…”

“…The influence of the leads’ spin polarization, the strength of coupling to the Majorana wire, and the overlap between the two edges of the nanowire have all been previously analyzed for systems consisting of a single quantum dot 53 . Those results are quantitatively relevant to the system under consideration in this study.…”

“…In particular, we study the current, differential conductance and cross-correlations between transport processes through the opposite edges of the system. Recent theoretical and experimental studies have shown that the current fluctuations and cross-correlations can reveal additional signatures of the presence of MZM in the system 44 – 53 . It is also important to note that similar models as studied in this paper have already been considered, however, mostly assuming noninteracting quantum dots, indicating that the analysis of fluctuations and, specifically, current cross-correlations provides extra insight into the Majorana physics 16 , 44 – 46 .…”

“…Moreover, we also examine the magnetoresistive properties of the system by exploiting ferromagnetic drains and resolving transport for wide range of the canting angle describing the spin-polarization of the Majorana edge states 58 . Interestingly, exploring the spin-selective transport characteristics have proved to be very useful in the context of Majorana polarization 53 , 59 – 63 or Majorana spintronics 64 . Furthermore, ferromagnetic contacts turned out to be crucial for detecting entanglement in a similar system with normal superconductor instead of a topological one 65 – 67 .…”