1,736 research outputs found
Quantum transport through a DNA wire in a dissipative environment
Electronic transport through DNA wires in the presence of a strong
dissipative environment is investigated. We show that new bath-induced
electronic states are formed within the bandgap. These states show up in the
linear conductance spectrum as a temperature dependent background and lead to a
crossover from tunneling to thermal activated behavior with increasing
temperature. Depending on the strength of the electron-bath coupling, the
conductance at the Fermi level can show a weak exponential or even an algebraic
length dependence. Our results suggest a new environmental-induced transport
mechanism. This might be relevant for the understanding of molecular conduction
experiments in liquid solution, like those recently performed on poly(GC)
oligomers in a water buffer (B. Xu et al., Nano Lett 4, 1105 (2004)).Comment: 5 pages, 3 figure
Structural fluctuations and quantum transport through DNA molecular wires: a combined molecular dynamics and model Hamiltonian approach
Charge transport through a short DNA oligomer (Dickerson dodecamer) in
presence of structural fluctuations is investigated using a hybrid
computational methodology based on a combination of quantum mechanical
electronic structure calculations and classical molecular dynamics simulations
with a model Hamiltonian approach. Based on a fragment orbital description, the
DNA electronic structure can be coarse-grained in a very efficient way. The
influence of dynamical fluctuations arising either from the solvent
fluctuations or from base-pair vibrational modes can be taken into account in a
straightforward way through time series of the effective DNA electronic
parameters, evaluated at snapshots along the MD trajectory. We show that charge
transport can be promoted through the coupling to solvent fluctuations, which
gate the onsite energies along the DNA wire
Complex microwave conductivity of Na-DNA powders
We report the complex microwave conductivity, , of
Na-DNA powders, which was measured from 80 K to 300 K by using a microwave
cavity perturbation technique. We found that the magnitude of near
room temperature was much larger than the contribution of the surrounding water
molecules, and that the decrease of with decreasing temperature was
sufficiently stronger than that of the conduction of counterions. These results
clearly suggest that the electrical conduction of Na-DNA is intrinsically
semiconductive.Comment: 16 pages, 7 figure
Localization Properties of Electronic States in Polaron Model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers
We numerically investigate localization properties of electronic states in a
static model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with
realistic parameters obtained by quantum-chemical calculation. The randomness
in the on-site energies caused by the electron-phonon coupling are completely
correlated to the off-diagonal parts. In the single electron model, the effect
of the hydrogen-bond stretchings, the twist angles between the base pairs and
the finite system size effects on the energy dependence of the localization
length and on the Lyapunov exponent are given. The localization length is
reduced by the influence of the fluctuations in the hydrogen bond stretchings.
It is also shown that the helical twist angle affects the localization length
in the poly(dG)-poly(dC) DNA polymer more strongly than in the
poly(dA)-poly(dT) one. Furthermore, we show resonance structures in the energy
dependence of the localization length when the system size is relatively small.Comment: 6 pages, 6 figure
Rate-equation calculations of the current flow through two-site molecular device and DNA-based junction
Here we present the calculations of incoherent current flowing through the
two-site molecular device as well as the DNA-based junction within the
rate-equation approach. Few interesting phenomena are discussed in detail.
Structural asymmetry of two-site molecule results in rectification effect,
which can be neutralized by asymmetric voltage drop at the molecule-metal
contacts due to coupling asymmetry. The results received for poly(dG)-poly(dC)
DNA molecule reveal the coupling- and temperature-independent saturation effect
of the current at high voltages, where for short chains we establish the
inverse square distance dependence. Besides, we document the shift of the
conductance peak in the direction to higher voltages due to the temperature
decrease.Comment: 12 pages, 6 figure
Optical absorption in semiconductor quantum dots: Nonlocal effects
The optical absorption of a single spherical semiconductor quantum dot in an
electrical field is studied taking into account the nonlocal coupling between
the field of the light and the polarizability of the semiconductor. These
nonlocal effects lead to a small size anf field dependent shift and broadening
of the excitonic resonance which may be of interest in future high precision
experiments.Comment: 6 pages, 4 figure
The low-energy electron point source microscope as a tool for transport measurements of free-standing nanometer scale objects: application to carbon nanotubes
We have developed a simple and reliable technique for two-terminal transport
measurements of free-standing wire-like objects. The method is based on the
low-energy electron point source microscope. The field emission tip of the
microscope is used as a movable electrode to make a well-defined local
electrical contact on a controlled place of a nanometer-size object. This
allows transport measurements of the object to be conducted. The technique was
applied to carbon nanotube ropes.Comment: 4 pages, 4 figures; submitted to J. Vac. Sci. Tech.
Polarons with a twist
We consider a polaron model where molecular \emph{rotations} are important.
Here, the usual hopping between neighboring sites is affected directly by the
electron-phonon interaction via a {\em twist-dependent} hopping amplitude. This
model may be of relevance for electronic transport in complex molecules and
polymers with torsional degrees of freedom, such as DNA, as well as in
molecular electronics experiments where molecular twist motion is significant.
We use a tight-binding representation and find that very different polaronic
properties are already exhibited by a two-site model -- these are due to the
nonlinearity of the restoring force of the twist excitations, and of the
electron-phonon interaction in the model. In the adiabatic regime, where
electrons move in a {\em low}-frequency field of twisting-phonons, the
effective splitting of the energy levels increases with coupling strength. The
bandwidth in a long chain shows a power-law suppression with coupling, unlike
the typical exponential dependence due to linear phonons.Comment: revtex4 source and one eps figur
Vibrational Enhancement of the Effective Donor - Acceptor Coupling
The paper deals with a simple three sites model for charge transfer phenomena
in an one-dimensional donor (D) - bridge (B) - acceptor (A) system coupled with
vibrational dynamics of the B site. It is found that in a certain range of
parameters the vibrational coupling leads to an enhancement of the effective
donor - acceptor electronic coupling as a result of the formation of the
polaron on the B site. This enhancement of the charge transfer efficiency is
maximum at the resonance, where the effective energy of the fluctuating B site
coincides with the donor (acceptor) energy.Comment: 5 pages, 3 figure
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