Temperature and magnetic field effects on electron transport through DNA molecules in a two-dimensional four-channel system.

We utilize a two-dimensional four-channel DNA model, with a tight-binding (TB) Hamiltonian, and investigate the temperature and the magnetic field dependence of the transport behavior of a short DNA molecule. Random variation of the hopping integrals due to the thermal structural disorder, which partially destroy phase coherence of electrons and reduce quantum interference, leads to a reduction of the localization length and causes suppressed overall transmission. We also incorporate a variation of magnetic field flux density into the hopping integrals as a phase factor and observe Aharonov-Bohm (AB) oscillations in the transmission. It is shown that for non-zero magnetic flux, the transmission zero leaves the real-energy axis and moves up into the complex-energy plane. We also point out that the hydrogen bonds between the base pair with flux variations play a role to determine the periodicity of AB oscillations in the transmission.

Resonance and phase shift in an open Aharonov-Bohm ring with an embedded quantum dot.

The transmission and phase properties of electron transport through a quantum dot (QD) with variable coupling to a third-terminal probe are investigated analytically for the case of the QD connected directly to source and drain reservoirs and when the QD is embedded in one arm of an Aharonov-Bohm (AB) ring. Using the tight-binding model, explicit analytical expressions of the transmission through the QD for each case are given. Expressions for the conductance with coupling to the third terminal, which breaks unitarity and phase-locking, are also given. It is shown that in a three-terminal interferometer the zero of the Fano resonance in the transmission moves off the real energy axis for finite values of the coupling parameter. The zero orbits around the pole in the complex energy plane as a function of magnetic flux through the ring, and can be returned to the real energy axis unless the coupling parameter exceeds a critical value. With the QD embedded in one arm of the AB ring, the electron transmission and the transmission phase, and the phase of the AB oscillations, are described in relation to the degree of coupling to the third-terminal probe which opens the interferometer. By tuning the degree of coupling to the probe, it is shown that the phase of the AB oscillations can be made to match the intrinsic phase of the QD, facilitating experimental characterization of the phase response of the QD.

Localization of phonon polaritons in disordered polar media.

The localization of the hybrid modes of phonons and photons in polar matter is investigated in the presence of random scatterers theoretically. We employ the self-consistent generalized Born-Huang approach to derive effective equations describing the phonon-polariton fields. Based on these equations, the density of states and various localization properties are exploited in two-dimensional systems both analytically and numerically within the framework of the Anderson model with a non-Hermitian effective Hamiltonian. Consequently, it is shown that the disorder effect brings some intriguing features which include the appearance of the localized states in the polariton bottleneck in the energy spectrum and the collapse of the energy gap. In addition, an analysis is given of the polariton level-spacing distribution.