Enhanced current rectification in graphene nanoribbons: effects of geometries and orientations of nanopores.

We discuss the possibility of getting rectification operation in graphene nanoribbon (GNR). For a system to be a rectifier, it must be physically asymmetric and we induce the asymmetry in GNR by introducing nanopores. The rectification properties are discussed for differently structured nanopores. We find that shape and orientation of the nanopores are critical and sensitive to the degree of current rectification. As the choice of Fermi energy is crucial for obtaining significant current rectification, explicit dependence of Fermi energy on the degree of current rectification is also studied for a particular shape of the nanopore. Finally, the role of nanopore size and different spatial distributions of the electrostatic potential profile across the GNR are explored. The stability of the nanopores is also discussed with a possible solution. Given the simplicity of the proposed method and promising results, the present proposition may lead to a new route of getting current rectification in different kinds of materials where nanopores can be formed selectively.

Efficient current rectification in driven acenes.

We examine the current-voltage (I-V) characteristics of different polyacenes, such as anthracene, tetracene, pentacene, etc., under the influence of arbitrarily polarized light. The irradiation effect produces an anisotropy in the system and acenes may therefore be employed as molecular rectifiers. We find that the rectification efficiency can be more than 90% with a specific set of light parameters. The phase of rectification (positive or negative) can suitably be engineered by controlling the light conditions. The effect of light irradiation is incorporated through the Floquet-Bloch ansatz with the minimal coupling scheme. The transport properties are calculated using Green's function technique following the Landauer-Büttiker formalism. Given the promising rectification results, the present prescription may be useful in designing functional elements, employing several other single/complex molecular structures in digital circuit design with the possibility of immense applications.

Strain-induced thermoelectricity in pentacene.

The present work discusses a non-synthetic strategy to achieve a favorable thermoelectric response in pentacene via strain. It is found that a uni-axial strain is capable of inducing spatial anisotropy in the molecule. As a result, the transmission spectrum becomes highly asymmetric under a particular strained scenario, which is the primary requirement to get a favorable thermoelectric response. Different thermoelectric quantities are computed for the strain-induced pentacene using Green's function formalism following the Landauer-Büttiker prescription. Various scenarios are considered to make the present work more realistic, such as the effects of substrate, coupling strength between the molecule and electrodes, dangling bonds, etc. Such a scheme to enhance the thermoelectric performance in pentacene is technologically intriguing and completely new to the best of our knowledge.

Phenomenon of multiple reentrant localization in a double-stranded helix with transverse electric field.

The present work explores the potential for observing multiple reentrant localization behavior in a double-stranded helical (DSH) system, extending beyond the conventional nearest-neighbor hopping (NNH) interaction. The DSH system is considered to have hopping dimerization in each strand, while also being subjected to a transverse electric field. The inclusion of an electric field serves the dual purpose of inducing quasi-periodic disorder and strand-wise staggered site energies. Two reentrant localization regions are identified: one exhibiting true extended behavior in the thermodynamic limit, while the second region shows quasi-extended characteristics with partial spreading within the helix. The DSH system exhibits three distinct single-particle mobility edges linked to localization transitions present in the system. The analysis in this study involves examining various parameters such as the single-particle energy spectrum, inverse participation ratio, local probability amplitude, and more. Our proposal, combining achievable hopping dimerization and induced correlated disorder, presents a unique opportunity to study phenomenon of reentrant localization, generating significant research interest.

Electrical analogue of one-dimensional and quasi-one-dimensional Aubry-André-Harper lattices.

This work explores the potential for achieving correlated disorder in electrical circuits by utilizing reactive elements. By establishing a direct correspondence between the tight-binding Hamiltonian and the admittance matrix of the circuit, a novel approach is presented. The localization phenomena within the circuit are investigated through the analysis of the two-port impedance. To introduce correlated disorder, the Aubry-André-Harper (AAH) model is employed. Both one-dimensional and quasi-one-dimensional AAH structures are examined and effectively mapped to their tight-binding counterparts. Notably, transitions from a high-conducting phase to a low-conducting phase are observed in these circuits, highlighting the impact of correlated disorder.

Interplay between hopping dimerization and quasi-periodicity on flux-driven circular current in an incommensurate Su-Schrieffer-Heeger ring.

We report for the first time the phenomenon of flux-driven circular current in an isolated Su-Schrieffer-Heeger (SSH) quantum ring in presence of cosine modulation in the form of the Aubry-André-Harper (AAH) model. The quantum ring is described within a tight-binding framework, where the effect of magnetic flux is incorporated through Peierls substitution. Depending on the arrangements of AAH site potentials we have two different kinds of ring systems that are referred to as staggered and non-staggered AAH SSH rings. The interplay between the hopping dimerization and quasiperiodic modulation leads to several new features in the energy band spectrum and persistent current which we investigate critically. An atypical enhancement of current with increasing AAH modulation strength is obtained that gives a clear signature of transition from a low conducting phase to a high conducting one. The specific roles of AAH phase, magnetic flux, electron filling, intra- and inter-cell hopping integrals, and ring size are discussed thoroughly. We also study the effect of random disorder on persistent current with hopping dimerization to compare the results with the uncorrelated ones. Our analysis can be extended further in studying magnetic responses of similar kinds of other hybrid systems in presence of magnetic flux.

Properties of the non-Hermitian SSH model: role ofPTsymmetry.

The present work addresses the distinction between the topological properties ofPTsymmetric and non-PTsymmetric scenarios for the non-Hermitian Su-Schrieffer-Heeger model. The non-PTsymmetric case is represented by non-reciprocity in both the inter- and the intra-cell hopping amplitudes, while the one withPTsymmetry is modeled by a complex on-site staggered potential. In particular, we study the loci of the exceptional points, the winding numbers, band structures, and explore the breakdown of bulk-boundary correspondence (BBC). We further study the interplay of the dimerization strengths on the observables for these cases. The non-PTsymmetric case denotes a more familiar situation, where the winding number abruptly changes by half-integer through tuning of the non-reciprocity parameters, and demonstrates a complete breakdown of BBC, thereby showing non-Hermitian skin effect. The topological nature of thePTsymmetric case appears to follow closely to its Hermitian analogue, except that it shows unbroken (broken) regions with complex (purely real) energy spectra, while another variant of the winding number exhibits a continuous behavior as a function of the strength of the potential, while the conventional BBC is preserved.

Spin-dependent transport in a driven non-collinear antiferromagnetic fractal network.

Non-collinear magnetic texture breaks the spin-sublattice symmetry which gives rise to a spin-splitting effect. Inspired by this, we study the spin-dependent transport properties in a non-collinear antiferromagnetic fractal structure, namely, the Sierpinski Gasket (SPG) triangle. We find that though the spin-up and spin-down currents are different, the degree of spin polarization is too weak. Finally, we come up with a proposal, where the degree of spin polarization can be enhanced significantly in the presence of a time-periodic driving field. Such a prescription of getting spin-filtering effect from an unpolarized source in a fractal network is completely new to the best of our knowledge. Starting from a higher generation of SPG to smaller ones, the precise dependencies of driving field parameters, spin-dependent scattering strength, interface sensitivity on spin polarization are critically investigated. The spatial distribution of spin-resolved bond current density is also explored. Interestingly, our proposed setup exhibits finite spin polarization for different spin-quantization axes. Arbitrarily polarized light is considered and its effect is incorporated through Floquet-Bloch ansatz. All the spin-resolved transport quantities are computed using Green's function formalism following the Landauer-Büttiker prescription. In light of the experimental feasibility of such fractal structures and manipulation of magnetic textures, the present work brings forth new insights into spintronic properties of non-collinear antiferromagnetic SPG. This should also entice the AFM spintronic community to explore other fractal structures with the possibility of unconventional features.

A new prescription to achieve a high degree of spin polarization in a spin-orbit coupled quantum ring: efficient engineering by irradiation.

The present work discusses the possibility to achieve a high degree of spin polarization in a three-terminal quantum system. Irradiating the system, subjected to Rashba spin-orbit (SO) interaction, we find high degree of spin polarization under a suitable input condition along with different magnitudes and phases at the two output leads. The system is described within a tight-binding (TB) framework and the effect of irradiation is incorporated following the Floquet-Bloch (FB) ansatz. All the spin-dependent transmission probabilities are evaluated through Green's function technique using Landauer-Büttiker formalism. Several possible aspects are included to make the system more realistic and examined rigorously in the present work. To name a few, the effects of irradiation, SO interaction, interface sensitivity, system size, system temperature are investigated, and finally, the role of correlated impurities are studied. Despite having numerous proposals available to generate and manipulate spin-selective transmissions, such a prescription exploiting the irradiation effect is relatively new to the best of our concern.

Possible route to efficient thermoelectric applications in a driven fractal network.

An essential attribute of many fractal structures is self-similarity. A Sierpinski gasket (SPG) triangle is a promising example of a fractal lattice that exhibits localized energy eigenstates. In the present work, for the first time we establish that a mixture of both extended and localized energy eigenstates can be generated yeilding mobility edges at multiple energies in presence of a time-periodic driving field. We obtain several compelling features by studying the transmission and energy eigenvalue spectra. As a possible application of our new findings, different thermoelectric properties are discussed, such as electrical conductance, thermopower, thermal conductance due to electrons and phonons. We show that our proposed method indeed exhibits highly favorable thermoelectric performance. The time-periodic driving field is assumed through an arbitrarily polarized light, and its effect is incorporated via Floquet-Bloch ansatz. All transport phenomena are worked out using Green's function formalism following the Landauer-Büttiker prescription.

Electronic transport through a driven quantum wire: possible tuning of junction current, circular current and induced local magnetic field.

We propose a new route of getting controlled electron transmission through a molecular wire having a single loop geometry, by irradiating the loop with an arbitrarily polarized light. Along with conventional junction current, a new current called bias driven circular current can be established in the loop under certain conditions depending on the junction configuration. This current, on the other hand, induces a strong magnetic field that can even reach to few tesla. All the physical phenomena can be regulated selectively by adjusting the irradiation parameters. In addition, we put forward another new route of regulating transport behavior by introducing a new path due to the proximity of the contact electrodes for a typical junction configuration. Employing a tight-binding framework, we include the effect of light irradiation within a minimal coupling scheme following the well known Floquet ansatz. Using the wave-guide theory we compute two-terminal transmission probability, and the currents are determined through the Landauer-Büttiker formalism. The present analysis may be utilized to investigate transport phenomena in any other molecular wires as well as tailor-made geometries having simple and/or complex loop sub-structures.