Biomedical subjects

Stephan Roche

Publications and source records attributed to Stephan Roche.

7 recordsLinked to original sources

PubMed2006

Inelastic quantum transport and peierls-like mechanism in carbon nanotubes.

We report on a theoretical study of inelastic quantum transport in (3m,0) carbon nanotubes. By using a many-body description of the electron-phonon interaction in Fock space, a novel mechanism involving optical phonon emission (absorption) is shown to induce an unprecedented energy-gap opening at half the phonon energy, variant Planck's over 2piomega0/2, above (below) the charge neutrality point. This mechanism, which is prevented by Pauli blocking at low bias voltages, is activated at bias voltages on the order of variant Planck's over 2piomega0.

Journal Article↗

PubMed2005

Anomalous magnetotransport in chemically doped carbon nanotubes.

We report on anomalous magnetotransport features in chemically doped, weakly disordered carbon nanotubes. Under the application of a magnetic field parallel to the tube axis, hole conduction is shown to be strongly affected by impurity scattering with short mean free path and negative magnetoresistance, strongly different from electron conduction with much longer mean free path and positive magnetoresistance behavior.

Journal Article↗

PubMed2005

Quantum dephasing in carbon nanotubes due to electron-phonon coupling.

We report on the effect of electron-phonon coupling on quantum transport in carbon nanotubes. The vibrational atomic displacements as well as the electron-phonon coupling strength are introduced through a time-dependent perturbation of the pi-electron Hamiltonian. The effect of dephasing on the Kubo conductance is studied for metallic and semiconducting nanotubes, and from a phenomenological law, coherence length (time) scales are found to fluctuate within the range 10 to 150 nm (0.01 to 4 ps) depending on the energy of charge carriers and phonon amplitude.

Journal Article↗

PubMed2005

Electronic transport in carbon nanotubes with random coverage of physisorbed molecules.

The chemical sensitivity of electronic transport in carbon nanotubes under the physisorption of molecular species is investigated using a tight-binding scheme, parametrized by first-principles calculations. Such a computational method enables tackling of the complex electronic properties of chemically grafted conducting nanotubes. Our calculations demonstrate that the impact of physisorption on the transport regime critically depends on the HOMO-LUMO gap of the attached molecules. In addition, the electronic mean free path exhibits a downscaling law with a lower dependence on the coverage density of grafted molecules than for conventional substitutional doping or homogeneous disorder.

Journal Article↗

PubMed2004

Mesoscopic transport in chemically doped carbon nanotubes.

Electronic quantum transport is investigated in boron- and nitrogen-doped carbon nanotubes using tight-binding methods correlated to ab initio calculations. The present technique accurately accounts for both effects of dopants, namely, charge transfer and elastic scattering. Generic transport properties such as conduction mechanisms, mean-free paths, and conductance scalings are derived for various concentration of randomly distributed boron and nitrogen dopants. Our calculations allow direct comparison with experiments and demonstrate that a small amount of dopants (<0.5%) can drastically modify the electronic transport properties of the tube, which is certainly a key effect feature for envisioning nanoelectronics.

Journal Article↗

PubMed2003

Long range correlations in DNA: scaling properties and charge transfer efficiency.

We address the relation between long-range correlations and charge transfer efficiency in aperiodic artificial or genomic DNA sequences. Coherent charge transfer through the highest occupied molecular orbital states of the guanine nucleotide is studied using the transmission approach, and the focus is on how the sequence-dependent backscattering profile can be inferred from correlations between base pairs.

Chromosomes, Human, Pair 22↗

PubMed2003

Sequence dependent DNA-mediated conduction.

We report on coherent charge transport studies in periodic Poly(dG)-Poly(dC) and aperiodic lambda-phage DNA sequences. The extent and efficiency of charge transfer is discussed as a function of sequence dependent energetics, of temperature dependent base-base couplings, and in relation with experiments.

Bacteriophage lambda↗