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We investigate the spin-polarized electron transport through a quantum ring whose arms are embedded by one protein-like single-helical molecule and one quantum dot, respectively. It is found that the inter-arm quantum interference leads to the enhancement of the spin polarization in this structure. Moreover, when local magnetic flux is applied through the ring, the spin polarization in the electron transport process, including the polarization strength and direction, can be further adjusted. Next in the finite-bias case, the spin polarization is also apparent and can be tuned by changing the magnetic flux or the dot level. This work provides a new scheme to manipulate the spin transport based on the single-helical molecule. [ABSTRACT FROM AUTHOR]

Motivated by the result in the recent work [A. Slachter, F. L. Bakker, J.-P. Adam, and B. J. van Wees, Nature Phys. 6, 879 (2010)], we research the thermally driven electron transport through a quantum dot (QD) coupled to two ferromagnetic leads and one normal-metallic lead. By applying temperature bias between the two ferromagnetic leads, we calculate the charge and spin currents in the normal-metallic lead and the spin accumulation in the QD. As a result, we observe that the charge and pure spin currents in the normal-metallic lead, as well as the spin accumulation in the QD, can be independently driven by the temperature bias. According to these results, we propose this system to be a promising candidate of the nanoswitch for the charge and spin current manipulation. [ABSTRACT FROM AUTHOR]

The Fano effect in electron transport through a parallel-coupled multi-quantum-dot system is theoretically studied by adjusting the asymmetries of dot-lead couplings. As a result, we find that three kinds of Fano lineshapes emerge in the linear conductance spectra. Namely, when the dot-lead couplings are up-down asymmetric, two kinds of Fano effects occur with the tuning of local magnetic fluxes. The other Fano effect is observed in the case of left-right asymmetry of the dot-lead couplings, which is tightly dependent on the dot number. We then transform the Hamiltonian into molecular orbital representation and discuss the three kinds of Fano interference mechanisms in detail. It is observed that the coupling manners between the leads and molecular states are the key factors to induce the Fano antiresonance. Since the abundant Fano effects, we consider such a structure to be a candidate of a thermoelectric device. We believe that the numerical results help to understand the Fano effect of the parallel-coupled multi-quantum-dot structure. [ABSTRACT FROM AUTHOR]

Spin-polarized electron transport through the zigzag graphene nanoribbon (ZGNR) is investigated by assuming that it couples with different charomium triiodide (CrI3) geometries, respectively. That is to say that the ZGNR either absorbs the monolayer CrI3 or one CrI3 molecule, or couples laterally with one CrI3 molecule. It is found that the spin polarization in the electron transport process is tightly dependent on the CrI3 geometry and the ZGNR-CrI3 coupling manner. When the CrI3 molecule is absorbed on the surface of the ZGNR, the spin-polarization efficiency is much higher than the other two cases, accompanied by the wide spin-polarization region. This work provides a new kind of scheme for optimizing the spin polarization in graphene-based materials. [ABSTRACT FROM AUTHOR]

The impurity-modulated electron transport properties in a double quantum dot (QD) Aharonov-Bohm ring are theoretically studied, by considering impurities locally and nonlocally coupled to the QDs in the ring arms, respectively. It is found that the impurities influence the electron transport in a nontrivial way: in the case of zero magnetic flux, a single-level impurity leads to the appearance of Fano line shapes in the conductance spectra, and the positions of Fano antiresonances are determined by both the impurity-QD couplings and the QD levels separated from the Fermi level; whereas when a magnetic flux is introduced with the phase factor [lowercase_phi_synonym]=π the Breit-Wigner line shapes appear in the conductance curves. Compared with the local-impurity case, nonlocal impurities alter the conductance period versus the magnetic flux. In addition, when many-body effect is considered within the second-order approximation, we find the important role of the Coulomb interaction in modifying the electron transport. [ABSTRACT FROM AUTHOR]

We report a theoretical study about the spin-dependent electron transport through a two-arm mesoscopic circuit in which two protein-like single-helical molecules connect serially with two normal metallic leads, respectively. Based on an effective-model Hamiltonian, the spin polarization is evaluated using the Landauer-Büttiker formula. Our results reveal that in comparison with the single-arm case, the spin-polarization efficiency can be enhanced in this system, by adjusting the length ratio of two molecules and the molecule-lead coupling manner. Besides, when local magnetic flux is introduced, the Aharonov-Bohm effect makes a nontrivial contribution to the spin polarization. These findings can be helpful for building the helical-molecule-based spin filters. [ABSTRACT FROM AUTHOR]

We investigate the electron transport through a quantum dot connected with two ferromagnetic leads, by coupling one Majorana doublet laterally to the quantum dot. It is found that Majorana doublet keeps the value of zero-bias conductance to be independent of the shift of structural parameters, including dot level, relative lead-magnetization direction, and magnetic field on the dot. Even in the cases of asymmetric dot-lead couplings, the zero-bias conductance is weakly dependent on the relative lead-magnetization direction. On the other hand, when Majorana doublet is replaced by Majorana singlet, the zero-bias conductance value becomes sensitive to the structural parameters. Via analyzing the respective particle motion processes, the different influences of Majorana doublet and singlet are explained. We believe that this work can be helpful for understanding the peculiar properties of Majorana doublet. [ABSTRACT FROM AUTHOR]

We investigate the electron transport through a graphene quantum dot with one line defect, by coupling the dot to two normal metallic leads. It is found that in the cases of the leads coupling to the same-type edges of the dot, the presence of line defect enhances the conductance at the Dirac point by inducing a new conductance peak or strengthening the original conductance peak. Such results are irrelevant to the graphene dot size. On the other hand, if the leads couple to the different-type edges of the dot, the line defect will induce two new conductance peaks near the Dirac point. The conductance enhancement is considered to originate from the fact that one bound state at the Dirac point induced by the line defect couples to the leads, which provides an additional channel for electron motion. Nevertheless, different dot-lead coupling manners change the contribution of the new channel to the electron motion, leading to the complicated transport results. These results show that the line-defect-existed graphene quantum dot will be beneficial to the realization of electron transport manipulation. [ABSTRACT FROM AUTHOR]

We investigate the electron transport through the T-shaped quantum-dot (QD) structure theoretically, by coupling a Majorana zero mode to the terminal QD. It is found that in the double-QD configuration, the presence of the Majorana zero mode can efficiently dissolve the antiresonance point in the conductance spectrum while inducing a conductance peak to appear at the same energy position. In the case of asymmetric QD-lead coupling, such a valley-to-peak transition induced by the Majorana zero mode still exists. Next, we observe in the multi-QD case that at the zero-bias limit, the conductance values are always the same as the double-QD result, independent of the parity of the QD number. We believe that all these results can be helpful for understanding the properties of Majorana bound states. [ABSTRACT FROM AUTHOR]

Electronic transport through a protein-like single-helical molecule is theoretically studied. By introducing an additional terminal to couple to the molecule, we construct a two-channel mesoscopic circuit, and then calculate the charge and spin currents in the two drain terminals. It is found that in one drain terminal, one pure spin current has an opportunity to appear without any accompanying charge current. Besides, the polarization direction of the spin current can be inverted. With respect to the current in the other drain, it is also found to be highly polarized, with its polarization direction different from that in the other terminal. These results suggest that the protein-like single-helical molecule is a promising candidate for building the two-channel setup in spintronics. [ABSTRACT FROM AUTHOR]

• We investigate the spin-polarized transport assisted by protein-like single-helical molecules. • Spin polarization property and efficiency are dependent on the structural geometries of the systems. • As molecule is serially coupled to two leads, inter-lead coupling magnifies the spin polarization. • Polarization direction can be adjusted by introducing the local magnetic flux. • In the other geometries, no apparent spin polarization can be driven. We investigate the spin-polarized transport through the systems with protein-like single-helical molecules. It shows that the spin polarization property and efficiency tightly depend on the geometries of the systems of single-helical molecules. When one molecule is serially coupled to two leads, the inter-lead coupling assists to magnify the spin polarization efficiency, and the polarization direction can be adjusted by the local magnetic flux. However in the other geometries, no apparent spin polarization is driven, such as the T-shaped structure with inter-lead coupling and parallel coupled structures. These results reflect the nontrivial effect of structure-dependence quantum interference on the spin polarization driven by the single-helical molecule. [ABSTRACT FROM AUTHOR]

Abstract We perform the first-principle studies on electron transport through four-terminal MoS 2 nanoribbons. It is found that in such structures, insulating bands exist in the linear-conductance spectra of the nanoribbons with straight channels, which are related to the band gaps of the MoS 2 nanoribbons. However, nonzero transports are allowed to take place in the insulating-band region in the geometries with curved channels. This phenomenon can be attributed to the formation of edge states in the curved-channel structures. We believe that these results provide useful information for the manipulation of electron transport through MoS 2 nanoribbons. Highlights • We perform first-principle studies on electron transport through four-terminal MoS 2 nanoribbons. • Insulating bands exist in the spectra of linear conductance in the straight channels. • Finite transports are allowed to take place in the insulating-band region in the curved channels. • These results provide useful information for manipulating transport through MoS 2 nanoribbons. [ABSTRACT FROM AUTHOR]

We theoretically investigate the electronic transport through a parallel-coupled multi-quantum-dot system, in which the terminal dots of a one-dimensional quantum-dot chain are embodied in the two arms of an Aharonov–Bohm interferometer. It is found that in the structures of odd(even) dots, all their even(odd) molecular states have opportunities to decouple from the leads, and in this process antiresonance occurs which are accordant with the odd(even)-numbered eigenenergies of the sub-molecule without terminal dots. Next when Majorana zero modes are introduced to couple laterally to the terminal dots, the antiresonance and decoupling phenomena still co-exist in the quantum transport process. Such a result can be helpful in understanding the special influence of Majorana zero mode on the electronic transport through quantum-dot systems. [ABSTRACT FROM AUTHOR]

We investigate the Fano effect in electron transport through a parallel mesoscopic circuit, whose arms are embedded by one quantum dot and one Majorana zero mode (MZM), respectively. It is found that by adjusting the dot-lead and MZM-lead couplings, the Fano linshapes have opportunities to appear in the linear conductance spectra. However, they do not form at the cases of ϕ = n π ( ϕ is the phase factor of the local magnetic flux). It also shows that the Fano lineshapes can be reversed by changing the bias voltage. These results are important for describing the transport properties assisted by MZM. [ABSTRACT FROM AUTHOR]

We investigate the electron transport through a multiple T-shaped quantum-dot structure in which the dots in the main channel are coupled to additional dots by Majorana bound states (MBSs) at the ends of one topological-superconducting nanowires. Calculation results show that at the zero-bias limit, the transport behavior displays the interesting two-stage decoupling effect, when the additional-dot levels shift around the Fermi energy. Firstly, if the levels of such dots are the same as the Fermi energy, their-coupled MBSs will be decoupled from the other MBSs. This leads to various zero-bias conductance results which are determined by the different dot-MBS coupling manners. Next when these levels depart away from the Fermi energy, the MBS pairs will be decoupled from the main channel simultaneously, and this system becomes equivalent to the structure with serially-coupled quantum dots. The findings in this work provide new understanding about the interplay between the quantum dot and MBSs in driving the electron transport through quantum-dot systems. [ABSTRACT FROM AUTHOR]

We investigate the electron transport through one double-helical molecule with four terminals, by considering one terminal to be the source and others to be the drains. It is found that notable spin polarizations simultaneously occur during the processes of intra-chain electron tunneling and inter-chain electron reflection. More importantly, in these two processes, the spin polarizations always show similar strengths and opposite directions. Based on these results, we consider that the spin polarization and spin separation can be co-realized in this system. [ABSTRACT FROM AUTHOR]

We investigate the influences of the electron–phonon interaction on the transport properties of one quantum-dot system with a side-coupled Majorana zero mode (MZM). Our calculation results show that at the zero-temperature limit, the MZM-governed zero-bias conductance value can be magnified, dependent on the interplay between electron–phonon interaction and dot–MZM coupling. In the case of finite temperature, the electron–phonon interaction makes leading contributions to the suppression of the magnitude of zero-bias conductance, but the effect is different from the case of electron tunneling without MZM. We believe that this work can be helpful for understanding the signature of the MZM in electron transport through mesoscopic circuits. • We investigate the effect of the e–ph coupling on a quantum-dot system with MZM. • At zero temperature, zero-bias conductance can be magnified by dot–MZM coupling. • At finite temperature, e–ph interaction suppresses the zero-bias conductance. • The e–ph effect is different from the case of without MZM even at finite temperature. • This work helps to understand the signature of MZM in transport through mesoscopic circuits. [ABSTRACT FROM AUTHOR]