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Several proposals are available to get selective spin transmission through different nano-junctions and in all the cases the regulation is done either by applying a magnetic field or by tuning spin–orbit (SO) coupling. In the present work, we explore a separate scheme where the spin-dependent transport is regulated externally by irradiating a quantum ring that bridges the contact electrodes. This is a new proposal of generating spin selective transmission through a nano-junction, to the best of our knowledge. A high degree of spin polarization along with its phase alteration can be achieved by suitably adjusting the irradiation, circumventing the regulation of magnetic field and/or SO coupling. The effect of irradiation is included through the well-known Floquet-Bloch ansatz, where all the spin-dependent transport phenomena are worked out using Green’s function formalism following the Landauer–Büttiker prescription within a tight-binding framework. Precise dependencies of light irradiation, SO coupling, magnetic flux threaded by the ring, interface sensitivity, system temperature, and impurities on spin polarization are critically investigated. Our analysis may give a new platform for spin selective electron transmission and make it applicable to other complex nano-structured materials also. We strongly believe that the present proposal can be examined in a suitable laboratory.

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.

We study the charge and spin transport in a two terminal graphene nanoribbon (GNR) decorated with random Gold (Au) adatoms using a Kane-Mele model. Two commonly used GNRs, that is, the armchair graphene nanoribbon (AGNR) and the zigzag graphene nanoribbon (ZGNR) are compared and contrasted, which shows that in presence of Au adatoms, a somewhat robust 2e 2 /h conductance plateau occurs in the case of AGNR around the zero of the Fermi energy, while in ZGNR this plateau is fragile. We show that this flat plateau, having a conductance value 2e 2 /h, is not a hallmark signature of a topologically nontrivial quantum spin Hall (QSH) state. Further the conductance decreases by a small amount with the density of adatoms. On the other hand, the spin polarized conductance shows distinct features of enhanced conductivity with increasing Au adatom concentration. Further the fluctuations of the spin polarized conductance have features that carry striking resemblance with the charge conductance profile of the GNRs.

Spin dependent transport in a three-terminal graphene nanoribbon (GNR) is investigated in presence of Rashba spin-orbit interaction. Such a three-terminal structure is shown to be highly effective in filtering electron spins from an unpolarized source simultaneously into two output leads and thus can be used as an efficient spin filter device compared to a two-terminal one. The study of sensitivity of the spin-polarized transmission on the location of the outgoing leads results in interesting consequences and is explored in details. There exist certain symmetry relations between the two outgoing leads with regard to spin-polarized transport, especially when they are connected to the system in a particular manner. We believe that the prototype presented here can be realized experimentally and hence the results can also be verified.

The key requirement for an enhanced thermoelectric (TE) performance is the presence of asymmetry in transmission function. Focussing on this issue, we propose a unique idea to enhance TE performance in a graphene nanoribbon (GNR) that has not been explored so far to the best of our concern. In the present work, one part of the GNR is considered as a disordered region while the rest of the system is clean. Such an ordered-disordered separated structure yields more asymmetric transmission function over the conventional uniform disordered one. Finally, we include the effect of electron–electron (e–e) interaction to check whether it brings any non-trivial signature on TE performance. The e–e interaction is taken in the form of an on-site Hubbard model and we compute our results within a Hartree–Fock mean field approach. The results obtained in the present work exhibit quite remarkable TE performance along with some non-trivial features.

PACS 72.80.Vp -Electronic transport in graphene PACS 72.25.-b -Spin polarized transport PACS 73.63.-b -Electronic transport in nanoscale materials and structuresAbstract -We investigate a novel way to manipulate the spin polarized transmission in a two terminal zigzag graphene nanoribbon in presence of Rashba spin-orbit (SO) interaction with circular shaped cavity engraved into it. A usual technique to control the spin polarized transport behaviour of a nanoribbon can be achieved by tuning the strength of the SO coupling, while we show that an efficient engineering of the spin polarized transport properties can also be done via cavities of different radii engraved in the nanoribbon. Simplicity of the technique in creating such cavities in the experiments renders an additional handle to explore transport properties as a function of the location of the cavity in the nanoribbon. Further, a systematic assessment of the interplay of the Rashba interaction and the dimensions of the nanoribbon is presented. These results should provide useful input to the spintronic behaviour of such devices. In addition to the spin polarization, we have also included an interesting discussion on the charge transmission properties of the nanoribbon, where, in absence of any SO interaction a metal-insulator transition induced by the presence of a cavity is observed.

The present work addresses the distinction between the topological properties of PT symmetric and non-PT symmetric scenarios for the non-Hermitian Su-Schrieffer-Heeger (SSH) model. The non-PT symmetric case is represented by non-reciprocity in both the inter- and the intra-cell hopping amplitudes, while the one with PT symmetry 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-PT symmetric 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 the PT symmetric 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.