Possible Routes to Obtain Enhanced Magnetoresistance in a Driven Quantum Heterostructure with a Quasi-Periodic Spacer

In this work, we perform a numerical study of magnetoresistance in a one-dimensional quantum heterostructure, where the change in electrical resistance is measured between parallel and antiparallel configurations of magnetic layers. This layered structure also incorporates a non-magnetic spacer, subjected to quasi-periodic potentials, which is centrally clamped between two ferromagnetic layers. The efficiency of the magnetoresistance is further tuned by injecting unpolarized light on top of the two sided magnetic layers. Modulating the characteristic properties of different layers, the value of magnetoresistance can be enhanced significantly. The site energies of the spacer is modified through the well-known Aubry–André and Harper (AAH) potential, and the hopping parameter of magnetic layers is renormalized due to light irradiation. We describe the Hamiltonian of the layered structure within a tight-binding (TB) framework and investigate the transport properties through this nanojunction following Green’s function formalism. The Floquet–Bloch (FB) anstaz within the minimal coupling scheme is introduced to incorporate the effect of light irradiation in TB Hamiltonian. Several interesting features of magnetotransport properties are represented considering the interplay between cosine modulated site energies of the central region and the hopping integral of the magnetic regions that are subjected to light irradiation. Finally, the effect of temperature on magnetoresistance is also investigated to make the model more realistic and suitable for device designing. Our analysis is purely a numerical one, and it leads to some fundamental prescriptions of obtaining enhanced magnetoresistance in multilayered systems.

Speckle tweezers for manipulation of high and low refractive index micro-particles and nano-particle loaded vesicles

Several fundamental research and applications in biomedicine and microfluidics often require controlled manipulation of suspended micro- and nanoscale particles. Speckle tweezers (ST) by incorporating randomly distributed light fields have been used to control micro-particles with refractive indices higher than their medium and to perform manipulation tasks such as guiding and sorting. Indeed, compared to periodic potentials, ST represents a wider possibility to be operated for such tasks. Here, we extend the usefulness of ST into micro-particles of low index with respect to the surrounding. Repelling of such particles by high intensity regions into lower intensity regions makes them to be locally confined, and the confinement can be tuned by changing the average grain intensity and size of the speckle patterns. Experiments on polystyrenes and liposomes validate the procedure. Moreover, we show that ST can also manipulate the nano-particle (NP)-loaded liposomes. Interestingly, the different interactions of NP-loaded and empty liposomes with ST enable collective manipulation of their mixture using the same speckle pattern, which may be explained by inclusion of the photophoretic forces on NPs. Our results on the different behaviors between empty and non-empty vesicles may open a new window on controlling collective transportation of drug micro-containers along with its wide applications in soft matter.

Dark gap solitons in periodic nonlinear media with competing cubic-quintic nonlinearities

Solitons are nonlinear self-sustained wave excitations and probably among the most interesting and exciting emergent nonlinear phenomenon in the corresponding theoretical settings. Bright solitons with sharp peak and dark solitons with central notch have been well known and observed in various nonlinear systems. The interplay of periodic potentials, like photonic crystals and lattices in optics and optical lattices in ultracold atoms, with the dispersion has brought about gap solitons within the finite band gaps of the underlying linear Bloch-wave spectrum and, particularly, the bright gap solitons have been experimentally observed in these nonlinear periodic systems, while little is known about the underlying physics of dark gap solitons. Here, we theoretically and numerically investigate the existence, property and stability of one-dimensional gap solitons and soliton clusters in periodic nonlinear media with competing cubic-quintic nonlinearity, the higher-order of which is self-defocusing and the lower-order (cubic) one is chosen as self-defocusing or focusing nonlinearities. By means of the conventional linear-stability analysis and direct numerical calculations with initial perturbations, we identify the stability and instability areas of the corresponding dark gap solitons and clusters ones.

Spectral Analysis for One Class Non-Self-Adjoint Operators with Almost Periodic Potentials

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