Presence Of Line Defects Research Articles

Emergent Mechanics of Magnetic Skyrmions Deformed by Defects.

While magnetic skyrmions are often modeled as rigid particles, both experiments and micromagnetic simulations indicate their easy-to-deform characteristic, especially when their motion is restricted by defects. Here we establish a theoretical framework for the dynamics of magnetic skyrmions by incorporating the degrees of freedom related to deformation and predict well the current-driven dynamics of deformable skyrmions in the presence of line defects without any parameter fitting, where classical theories based on rigid-particle assumption deviate significantly. Further, we define an emergent property of magnetic skyrmions-flexibility and show that this property strongly modulates the depinning dynamics of skyrmions along a line defect with breaches. Our work explores the emergent mechanics of magnetic skyrmions and extends the current understanding on the dynamics of skyrmions interacted with defects.

Resonant tunneling in disordered borophene nanoribbons with line defects

Recently, borophene has attracted extensive interest as the wonder material, showing that line defects (LDs) occur widely at the interface between nu _{1/5} and nu _{1/6} boron sheets. Here, we study theoretically the electron transport through two-terminal disordered borophene nanoribbons (BNRs) with random distribution of LDs. Our results indicate that LDs strongly affect the electron transport properties of BNRs. Both nu _{1/5} and nu _{1/6} BNRs exhibit metallic behavior without any LD, in agreement with experiments. While in the presence of LDs, the overall electron transport ability is dramatically decreased, but some resonant peaks of conductance quantum are found in the transmission spectrum of any disordered BNR with arbitrary arrangement of LDs. These disordered BNRs exhibit metal-insulator transition with tunable transmission gap in the insulating regime. Furthermore, two evolution phenomena of resonant peaks are revealed for disordered BNRs with different widths. These results may help for understanding structure-property relationships and designing LD-based nanodevices.

Enhancement of thermoelectric performance of a nanoribbon made of lattice

We present electronic and transport properties of a zigzag nanoribbon made of lattice. Our particular focus is on the effects of the continuous evolution of the edge modes (from flat to dispersive) on the thermoelectric transport properties. Unlike the case of graphene nanoribbon, the zigzag nanoribbon of lattice can host a pair of dispersive edge modes at the two valleys for specific width of the ribbon. Moreover, gap opening can also occur at the two valleys depending on the width. The slope of the dispersive edge modes and the energy gap strongly depend on the relative strength of two kinds of hoping parameters present in the system. We compute corresponding transport coefficients such as conductance, thermopower, thermal conductance and the thermoelectric figure of merits by using the tight-binding Green function formalism, in order to explore the roles of the dispersive edge modes. It is found that the thermopower and thermoelectric figure of merits can be enhanced significantly by suitably controlling the edge modes. The figure of merits can be enhanced by thirty times under suitable parameter regime in comparison to the case of graphene. Finally, we reveal that the presence of line defect, close to the edge, can cause a significant impact on the edge modes as well as on electrical conductance and thermopower.

Effect of Line Defects on the Electrical Transport Properties of Monolayer MoS<inline-formula> <tex-math notation="LaTeX">$_{\bf 2}$</tex-math></inline-formula> Sheet

We present a computational study on the impact of line defects on the electronic properties of monolayer MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . Four different kinds of line defects with Mo and S as the bridging atoms, consistent with recent theoretical and experimental observations, are considered herein. We employ the density functional tightbinding (DFTB) method with a Slater-Koster-type DFTB-CP2K basis set for evaluating the material properties of perfect and the various defective MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sheets. The transmission spectra are computed with a DFTB-non-equilibrium Green's function formalism. We also perform a detailed analysis of the carrier transmission pathways under a small bias and investigate the phase of the transmission eigenstates of the defective MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sheets. Our simulations show a two to four fold decrease in carrier conductance of MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sheets in the presence of line defects as compared to that for the perfect sheet.

Fano effect and bound state in continuum in electron transport through an armchair graphene nanoribbon with line defect

Electron transport properties in an armchair graphene nanoribbon are theoretically investigated by considering the presence of line defect. It is found that the line defect causes the abundant Fano effects and bound state in continuum (BIC) in the electron transport process, which are tightly dependent on the width of the nanoribbon. By plotting the spectra of the density of electron states of the line defect, we see that the line defect induces some localized quantum states around the Dirac point and that the different localizations of these states lead to these two kinds of transport results. Next, the Fano effect and BIC phenomenon are detailedly described via the analysis about the influence of the structure parameters. According to the numerical results, we propose such a structure to be a promising candidate for graphene nanoswitch.PACS81.05.Uw, 71.55.-i, 73.23.-b, 73.25.+i

Positional dependence of energy gap on line defect in armchair graphene nanoribbons: Two-terminal transport and related issues

The characteristics of energy band spectrum of armchair graphene nanoribbons in the presence of line defect are analyzed within a simple non-interacting tight-binding framework. In metallic nanoribbons, an energy gap may or may not appear in the band spectrum depending on the location of the defect line, while in semiconducting ribbons, the gaps are customized, yielding the potential applicabilities of graphene nanoribbons in nanoscale electronic devices. With a more general model, we also investigate two-terminal electron transport using Green's function formalism.

Line-defect–induced Fano interference in an armchair graphene nanoribbon

Electron transport through a metallic armchair graphene nanoribbon is theoretically investigated by considering the presence of line defect. The line defect is formed by the staggered stacking of the pentagons and heptagons. Our calculation results show that the line defect mainly destroys the electron transport in the conduction-band region by inducing the abundant Fano effects in the electron transport process. Moreover, the properties of the Fano effects are tightly dependent on the width M of the nanoribbon, and the results of are completely different from those of M > 17. The spectra of the density of electron states illustrate that the line defect induces some localized quantum states, and that the different localizations of these states lead to the distinct transport results. By analyzing the influence of the structure parameters, the Fano effects are described in detail. All the results demonstrate that such a structure can be a promising candidate for electron manipulation in graphene nanoribbon.

Defect-induced resonances and magnetic patterns in graphene

We investigate the effects of point and line defects in monolayer graphene within the framework of the Hubbard model, using a self-consistent mean field theory. These defects are found to induce characteristic patterns into the electronic density of states and cause non-uniform distributions of magnetic moments in the vicinity of the impurity sites. Specifically, defect induced resonance bound states in the local density of states are observed at energies close to the Dirac points. The magnitudes of the frequencies of these resonance states are shown to decrease with the strength of the scattering potential, whereas their amplitudes decay algebraically with increasing distance from the defect. For the case of defect clusters, we observe that with increasing defect cluster size the local magnetic moments in the vicinity of the cluster center are strongly enhanced. Furthermore, non-trivial impurity induced magnetic patterns are observed in the presence of line defects: zigzag line defects are found to introduce stronger-amplitude magnetic patterns than armchair line defects. When the scattering strength of these topological defects is increased, the induced patterns of magnetic moments become more strongly localized.