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A double-stranded DNA molecule subject to a perpendicular gating electric field and a small mechanical strain exhibits a negative differential resistance (NDR) in its current–voltage (I–V) characteristics. Using an advanced two-dimensional tight-binding model including hopping integrals for the next nearest-neighbors, we implement perturbative strain- and tilted angle-dependent DNA helix conformation in conjunction with the theories of Slater–Koster and linear elasticity. The degree of NDR can be tuned by adjusting the tilt angle and mechanical strain of the DNA. This effect arises because of a surface charge distribution near the contacts due to the normal component of the electric field and structural change of the DNA molecule due to the strain. It is shown that enhancement of NDR peak current and a large peak-to-valley ratio of NDR are achieved by an increase of the tilt angle and stretching strain. Finally, a series of step-like current jumps without NDR features are exhibited in the weak DNA-lead coupling regime. This disappearance of NDR stems from the fact that reduced conduction through metal electrodes with a sufficiently small tunneling rate compensates the current drop.

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An advanced two-dimensional tight-binding model including the next nearest-neighbor effects for quantum mechanical electron transport through double-stranded DNA molecules is proposed. Considering the next nearest-neighbor hopping strengths between sites gives a more rational and realistic model for the electron path-way through DNA molecules. We show higher overall transmission and enhanced current for a 30 base-pair poly(G)–poly(C) DNA molecule with the inclusion of diagonal electron hopping between the sites. In addition, an optimum condition of the contact hopping strength and Fermi energy to obtain the maximum current for the system is demonstrated. Finally, we present the current-voltage characteristics showing a transition from a semiconductor-like to a metal-like DNA molecule with the variation of the Fermi energy.

We study spin-dependent transport and spin polarization through two asymmetric quantum dots (QD’s) embedded in the arms of an Aharonov-Bohm (AB) ring, in which spin splitting produced by external magnetic fields is incorporated into a tight-binding model Hamiltonian. This device shows a sensitive spin-polarization effect by manipulating either in-plane or perpendicular magnetic fields. In particular, an extremely small Zeeman splitting leads to a reversal of the polarization polarity in the differential weighted spin-polarization function. Finally, we demonstrate that the degree of spin polarization is affected by the additional AB effects in the ring. In comparison, the polarization is substantially lower through a single QD in a one-dimensional system.