843 research outputs found
Sample-specific and Ensemble-averaged Magnetoconductance of Individual Single-Wall Carbon Nanotubes
We discuss magnetotransport measurements on individual single-wall carbon
nanotubes with low contact resistance, performed as a function of temperature
and gate voltage. We find that the application of a magnetic field
perpendicular to the tube axis results in a large magnetoconductance of the
order of e^2/h at low temperature. We demonstrate that this magnetoconductance
consists of a sample-specific and of an ensemble-averaged contribution, both of
which decrease with increasing temperature. The observed behavior resembles
very closely the behavior of more conventional multi-channel mesoscopic wires,
exhibiting universal conductance fluctuations and weak localization. A
theoretical analysis of our experiments will enable to reach a deeper
understanding of phase-coherent one-dimensional electronic motion in SWNTs.Comment: Replaced with published version. Minor changes in tex
Correlation between molecular orbitals and doping dependence of the electrical conductivity in electron-doped Metal-Phthalocyanine compounds
We have performed a comparative study of the electronic properties of six
different electron-doped metal phthalocyanine (MPc) compounds (ZnPc, CuPc,
NiPc, CoPc, FePc, and MnPc), in which the electron density is controlled by
means of potassium intercalation. In spite of the complexity of these systems,
we find that the nature of the underlying molecular orbitals produce observable
effects in the doping dependence of the electrical conductivity of the
materials. For all the MPc's in which the added electrons are expected to
occupy orbitals centered on the ligands (ZnPc, CuPc, and NiPc), the doping
dependence of the conductivity has an essentially identical shape. This shape
is different from that observed in MPc materials in which electrons are also
added to orbitals centered on the metal atom (CoPc, FePc, and MnPc). The
observed relation between the macroscopic electronic properties of the MPc
compounds and the properties of the molecular orbitals of the constituent
molecules, clearly indicates the richness of the alkali-doped
metal-phthalocyanines as a model class of compounds for the investigation of
the electronic properties of molecular systems
High-performance -type organic field-effect transistors with ionic liquid gates
High-performance -type organic field-effect transistors were developed
with ionic-liquid gates and N,N-bis(n-alkyl)-(1,7 and
1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide)s single-crystals. Transport
measurements show that these devices reproducibly operate in ambient atmosphere
with negligible gate threshold voltage and mobility values as high as 5.0
cm/Vs. These mobility values are essentially identical to those measured in
the same devices without the ionic liquid, using vacuum or air as the gate
dielectric. Our results indicate that the ionic-liquid and -type organic
semiconductor interfaces are suitable to realize high-quality -type organic
transistors operating at small gate voltage, without sacrificing electron
mobility
Photon-assisted electron transport in graphene
Photon-assisted electron transport in ballistic graphene is analyzed using
scattering theory. We show that the presence of an ac signal (applied to a gate
electrode in a region of the system) has interesting consequences on electron
transport in graphene, where the low energy dynamics is described by the Dirac
equation. In particular, such a setup describes a feasible way to probe energy
dependent transmission in graphene. This is of substantial interest because the
energy dependence of transmission in mesoscopic graphene is the basis of many
peculiar transport phenomena proposed in the recent literature. Furthermore, we
discuss the relevance of our analysis of ac transport in graphene to the
observability of zitterbewegung of electrons that behave as relativistic
particles (but with a lower effective speed of light).Comment: 5 pages, 2 figure
Competition between Spin-Orbit Interaction and Zeeman Coupling in Rashba 2DEGs
We investigate systematically how the interplay between Rashba spin-orbit
interaction and Zeeman coupling affects the electron transport and the spin
dynamics in InGaAs-based 2D electron gases. From the quantitative analysis of
the magnetoconductance, measured in the presence of an in-plane magnetic field,
we conclude that this interplay results in a spin-induced breaking of time
reversal symmetry and in an enhancement of the spin relaxation time. Both
effects, due to a partial alignment of the electron spin along the applied
magnetic field, are found to be in excellent agreement with recent theoretical
predictions.Comment: 4 figures and 4 page
Influence of the gate leakage current on the stability of organic single-crystal field-effect transistors
We investigate the effect of a small leakage current through the gate
insulator on the stability of organic single-crystal field-effect transistors
(FETs). We find that, irrespective of the specific organic molecule and
dielectric used, leakage current flowing through the gate insulator results in
an irreversible degradation of the single-crystal FET performance. This
degradation occurs even when the leakage current is several orders of magnitude
smaller than the source-drain current. The experimental data indicate that a
stable operation requires the leakage current to be smaller than $10^{-9} \
\mathrm{A/cm}^2$. Our results also suggest that gate leakage currents may
determine the lifetime of thin-film transistors used in applications.Comment: submitted to Appl. Phys. Let
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