No abstract

The role of light irradiation on electronic localization is critically investigated for the first time in a tight-binding lattice where site energies are modulated in the cosine form following the Aubry-Andr\'{e}-Harper (AAH) model. The critical point of transition from delocalized-to-localized phase can be monitored selectively by regulating the light parameters that is extremely useful to have controlled electron transmission across the system. Starting with a strictly one-dimensional (1D) AAH chain, we extend our analysis considering a two-stranded ladder model which brings peculiar signatures in presence of irradiation. Unlike 1D system, AAH ladder exhibits a mixed phase (MP) zone where both extended and localized energy eigenstates co-exist. This is the fundamental requirement to have mobility edge in energy band spectrum. A mathematical description is given for decoupling the irradiated ladder into two effective 1D AAH chains. The underlying mechanism of getting a MP zone relies on the availability of two distinct critical points (CPs) of the decoupled chains, in presence of second-neighbor hopping between the two strands. Using a minimal coupling scheme the effect of light irradiation is incorporated following the Floquet-Bloch ansatz. The localization behaviors of different energy eigenstates are studied by calculating inverse participation ratio, and, are further explained in a more compact way by calculating two-terminal transmission probabilities together with average density of states. Finally, the decoupling procedure is extended for a more general multi-stranded AAH ladders where multiple critical points and thus multiple mobility edges are found. Our analysis may provide a new route of engineering localization properties in similar kind of other fascinating quasiperiodic systems.

In this work, we address the fundamental question of whether a magnetic material having zero net magnetization can produce polarized spin current from a completely unpolarized one. Common wisdom suggests that this is not possible, but if we break the symmetry in hopping integrals in different segments of the magnetic sample, then a finite possibility of getting polarized spin current is established. To substantiate this fact, we consider a one-dimensional magnetic chain with vanishing net magnetization where one part of the chain is subjected to an ac electric field, keeping the other part free. The ac field, introduced through Peierls substitution, modulates the hopping integrals yielding a misalignment of up and down spin channels, which is the primary requirement to get finite spin polarization. Simulating the system within a tight-binding framework, we compute spin-dependent transmission probabilities using the well-known Green’s function prescriptionand determine junction currents following the Landauer–Büttiker formalism. Our analysis may shed some light on designing spin-polarized devices using driven magnetic materials with vanishing net magnetization.

Spectral properties of a magnetic chain and spin dependent electron transport through it are critically examined in presence of light irradiation. Two different kinds of bonds, long and short are taken into account where each site of the chain is composed of a finite magnetic moment which yields spin dependent scattering to generate polarized currents from a unpolarized one. The degree of spin polarization and its phase can selectively be adjusted with the help of irradiation parameters. All the results are valid for a wide range of physical parameters which suggest that the present proposal can be verified through a suitable laboratory experiment.

The current rectification phenomenon is investigated at nanoscale level considering a one-dimensional tight-binding chain whose site energies are modulated in a cosine form following the well established Aubry-Andre-Harper (AAH) form in presence of a periodically driving field. The appearance of an electric field along the chain due to voltage bias leads to an asymmetry in the system, resulting in different currents in two bias polarities. The degree of current rectification can be monitored selectively by means of external light irradiation, which is included into the system by means of a minimal coupling scheme. Our analysis may provide a new direction of designing tunable currents rectifiers using AAH systems and other similar kinds of fascinating correlated disordered ones.