Quantum Devices Design Of Graphene Nanoribbon Based On Topological States

In this paper,based on the combination of density functional theory and the non-equilibrium Green function(NEGF-DFT),we systematically study the electronic structures and transport properties of the topological graphene nanoribbons(GNRs)by first-principles calculations.The main results were as follows:Here,we investigated the electronic structure and transport properties of 7/9-AGNRs constructed by alternating topologically trivial 7-AGNRs and topologically nontrivial 9-AGNRs segments.We find that the occupied topologically induced band(OTB)and unoccupied topologically induced band(UTB)are isolated in the gap and separated widely from the other non-topological bands.Their eigenvalues and spatial distributions are totally dominated by these lengths.As lengthening nontrivial segment,the OTB and UTB approach each other and shift to the Fermi level,makes the energy gap(E_g)highly tunable in a wide range from 0.04 to 1.14 eV.As lengthening trivial segment,the OTB and UTB transform from inter-segmental delocalization to intra-segmental localization,manipulates the conductivity.Surprisingly,the electron transport characteristics of the system are completely dominated by the single transmission channel formed by the coupled OTB and UTB,and show a robust negative differential resistance(NDR)with a high peak-to-valley current ratio(PVCR)up-to 10~4.In addition,the highly tunable E_g and the robust NDR are also found in the topological GNRs constructed by the trivial 7-AGNR and the nontrivial cove-edged GNR(A/C-GNRs).Therefore,we believe that the highly tunable E_g and robust NDR phenomena of topological GNRs are general.We discussed the magnetic properties of A/C-GNRs.The first-principle results indicate that there is spin polarization in A/C-GNRs.The net spin of it mainly distributed on the whole interface regions with well antiferromagnetic(AFM)coupling between the two opposite interface states.After further research,we found that the spin-polarized state in the system is neither from the edge state nor the terminal state,but from the interface state.Moreover,due to the interface states are derived from the coupled OTB and UTB,the topological phase is the only source of spin polarized states.In addition,we also found that the calculated magnetic moment of the systems is always 2?_B in integer and the Curie temperature is highly tunable.These characteristics are totally different from that of the spin-polarized states in zigzag GNRs,chiral GNRs and S-type A-GNRs.Therefore,the magnetism of the A/C-GNRs system is topologically induced interface magnetism,which is very robust.In conclusion,our findings provide clear evidence for the existence of topologically induced highly tunable energy gaps,robust negative differential conductance phenomena,and highly spin-polarized interface states,enriching GNR-based electrical and magnetic knowledge and having promising applications in the fields of quantum informatics,quantum computing and molecular electronics.