Papers by Keyword: Nanophysics

Abstract: The generalizations of the Drude model describe classically the most important quantities referred to transport phenomena, i.e the velocity correlation functions, the mean square deviation of position and the diffusion coefficient. The quantum effects, appearing in systems at nano-dimensions, require a quantum treatment of the previous models. I have presented a new ‘time-domain’ quantum mechanical model for transport in nanosystems, which comprehends the oscillator strength weights; this model demonstrates high generality and good application perspectives also in the study of ions, solutions, and in nano-bio-systems. This quantum mechanical extension allows to test the diffusion in nanostructured materials for biological, medical and nanopiezotronic devices. The theoretical elaboration of experimental data shows the interesting presence of an initial oscillating behaviour in velocity and an enhanced initial diffusivity, offering considerable informations for the experimental researchers.

Abstract: We analyze the effect of the geometrical shape and size of the cross section on the spin-polarized transport and the giant magnetoresistance (GMR) by a finite element method, and evaluate the stability and the physical properties of nano-scale spin valves. We calculate the transmission coefficients in the ballistic regime by using a transfer-matrix method, and evaluate the GMR of the current perpendicular to the plane (CPP) by using a circuit theory. The conduction-band structure is simplified to the potential step, which is determined by combining the interfacial parameters calculated by first-principles with the free electron model. The geometrical shapes of the cross section are line and square. As a result, the cross sectional shape has a significant effect on the spin-polarized transport and the GMR. The square-shaped cross section has an advantage of the large GMR, which is contrary to the line-shaped cross section. These phenomena result from the difference of the cut-off energies with the transverse modes and, consequently, the different spin-down transmission coefficients.