We propose a locally protected ladder-like atomic system (nanoconductor) on a substrate that is insensitive to external perturbations. The system corresponds to coupled atomic chains fabricated on different surfaces. Electron transport properties of such conductors are studied theoretically using the model tight-binding Su-Schriffer-Hegger (SSH) Hamiltonian and Green's function formalism. We have found that the conductance of the system is almost insensitive to single adatoms and oscillates as a function of the side chain length with very large periods. Non-local character of the electron transport was observed also for topological SSH chains where nontrivial end states survive in the presence of disturbances as well as for different substrates. We have found that the careful inspection of the density of states or charge waves can provide the information about the atom energy levels and hopping amplitudes. Moreover, the ladder-like geometry allows one to distinguish between normal and topological zero-energy states. It is important that topological chains do not reveal Friedel oscillations which are observed in non-topological chains.
Mid-gap 1D topological states and their electronic properties on different 2D hybrid structures are investigated using the tight binding Hamiltonian and the Green’s function technique. There are considered straight armchair-edge and zig-zag Su–Schrieffer–Heeger (SSH) chains coupled with real 2D electrodes which density of states (DOS) are characterized by the van Hove singularities. In this work, it is shown that such 2D substrates substantially influence topological states end evoke strong asymmetry in their on-site energetic structures, as well as essential modifications of the spectral density function (local DOS) along the chain. In the presence of the surface singularities the SSH topological state is split, or it is strongly localized and becomes dispersionless (tends to the atomic limit). Additionally, in the vicinity of the surface DOS edges this state is asymmetrical and consists of a wide bulk part together with a sharp localized peak in its local DOS structure. Different zig-zag and armachair-edge configurations of the chain show the spatial asymmetry in the chain local DOS; thus, topological edge states at both chain ends can appear for different energies. These new effects cannot be observed for ideal wide band limit electrodes but they concern 1D topological states coupled with real 2D hybrid structures.
Atomic ribbons and monoatomic chains on different substrates are proposed as spin-dependent electrical conductors with asymmetrical local density of states (DOS) and ferromagnetic occupancies along the chains. The tight-binding Hamiltonian and Green’s function techniques were used to analyze the electrical properties of both normal and topological systems with spin-orbit scattering. To make the system more realistic, electron leakage from atomic chains to various types of substrates is considered. We have shown that delocalized electrons in the substrate and spin-orbit interactions are responsible for asymmetry in the local DOS. The structure of DOS for spin-orbit nontopological chains is spin-dependent at both chain edges; however, in the middle of the chain, only paramagnetic solutions are observed. Additionally, we have found different periods of the local DOS oscillations along the chain in the presence of spin-flip and spin-orbit couplings. For topological chains, the edge nontrivial states split in the presence of spin-orbit scattering and spin-dependent Friedel oscillations appear along the whole topological chain. We have also found out-of-phase Friedel oscillations between neighboring chains along the atomic ribbon.
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