Gate-dependent magnetoresistance phenomena in carbon nanotubes

We report on the first experimental study of the magnetoresistance of double-walled carbon nanotubes under magnetic field as large as 50 Tesla. By varying the field orientation with respect to the tube axis, or by gate-mediated shifting the Fermi level position, evidences for unconventional magnetoresistance are presented and interpreted by means of theoretical calculations

Discrete quantum dot like emitters in monolayer MoSe2: Spatial mapping, Magneto-optics and Charge tuning

Transition metal dichalcogenide monolayers such as MoSe2,MoS2 and WSe2 are direct bandgap semiconductors with original optoelectronic and spin-valley properties. Here we report spectrally sharp, spatially localized emission in monolayer MoSe2. We find this quantum dot like emission in samples exfoliated onto gold substrates and also suspended flakes. Spatial mapping shows a correlation between the location of emitters and the existence of wrinkles (strained regions) in the flake. We tune the emission properties in magnetic and electric fields applied perpendicular to the monolayer plane. We extract an exciton g-factor of the discrete emitters close to -4, as for 2D excitons in this material. In a charge tunable sample we record discrete jumps on the meV scale as charges are added to the emitter when changing the applied voltage. The control of the emission properties of these quantum dot like emitters paves the way for further engineering of the light matter interaction in these atomically thin materials.Comment: 5 pages, 2 figure

Probing the electronic properties of individual carbon nanotube in 35 T pulsed magnetic field

After optimization of the alignment and the nano-contact processes of isolated single wall and double-walls carbon nanotube, we investigate the high magnetic field effects on the electronic transport properties of an individual metallic CNT. We develop pioneer multi-probes magneto-transport experiments under a 35 T pulsed field which reveal an unexpected oscillatory behavior of RðHÞ inconsistent with existing theories

Unconventional magnetotransport phenomena in individual carbon nanotubes

We investigate the quantum transport in different individual carbon nanotubes in the light of magneto-transport experiments in intense (60T pulsed)magnetic field. Large magnetic fields are required to probe field dependent gap modulation and quantum interference effects along the circumference of the tube. Such experiments along with a control of the electrostatic doping of the tube by a back-gate voltage constitute an unique tool to explore the exceptional electronic properties of this material. We bring evidence that the field dependence of the conductivity is a fingerprint of the electronic conduction modes and their interplay with the band structure (helicity), the static disorder and the location of the Fermi level of the tube. We infer the characteristic lengths of the electronic transport (the electronic mean free path and the phase coherence length) which are differently modified by the Fermi level location, depending on the disorder

Tuning Magnetic Properties of a Carbon Nanotube-Lanthanide Hybrid Molecular Complex through Controlled Functionalization

Molecular magnets attached to carbon nanotubes (CNT) are being studied as potential candidates for developing spintronic and quantum technologies. However, the functionalization routes used to develop these hybrid systems can drastically affect their respective physiochemical properties. Due to the complexity of this systems, little work has been directed at establishing the correlation between the degree of functionalization and the magnetic character. Here, we demonstrate the chemical functionalization degree associated with molecular magnet loading can be utilized for controlled tuning the magnetic properties of a CNT-lanthanide hybrid complex. CNT functionalization degree was evaluated by interpreting minor Raman phonon modes in relation to the controlled reaction conditions. These findings were exploited in attaching a rare-earth-based molecular magnet (Gd-DTPA) to the CNTs. Inductively coupled plasma mass spectrometry, time-of-flight secondary ion mass spectrometry and super conducting quantum interference device (SQUID) measurements were used to elucidate the variation of magnetic character across the samples. This controlled Gd-DTPA loading on the CNT surface has led to a significant change in the nanotube intrinsic diamagnetism, showing antiferromagnetic coupling with increase in the Weiss temperature with respect to increased loading. This indicates that synthesis of a highly correlated spin system for developing novel spintronic technologies can be realized through a carbon-based hybrid material

Transport électronique dans les nanotubes de carbone; étude sous champ magnétique

This thesis is devoted to the study of the electronic transport in carbon nanotubes. Inthis scheme, we combine a high magnetic field (60T) with an electrostatic control of theelectronic doping. The goal is to show the key role played by the energy band structureand the disorder. Several kind of metallic tubes with variable structural quality havebeen studied. Depending on the ratio between the elastic mean free path (le) and thenanotube circumference (L), different regimes appear. When le>L, a ballistic conduction is established and clearly shows the unique role of theband structure. A complete opening of the energy gap under magnetic field is observed(Aharonov-Bohm effect, AB). A simulation based on the Landauer formalism explainsthe prominent role of the Schottky barrier at the contacts. It is the first experimentalevidence of the Aharonov-Bohm Schottky barrier modulations.Cette thèse a pour objet l'étude du transport électronique dans les nanotubes de carbone grâce à l'utilisation combinée d'un fort champ magnétique (60T) et d'un contrôle électrostatique du dopage électronique. Il s'agit alors de montrer les rôles clés joués par la structure de bande en énergie et par le désordre. Plusieurs types de tubes métalliques de qualité structurale variable ont été étudiés. Selon le rapport entre le libre parcours moyen élastique (le) et la circonférence du nanotube (L), différents régimes apparaissent. Lorsque l

Transport électronique dans les nanotubes de carbone, étude sous champ magnétique

Cette thèse a pour objet l'étude du transport électronique dans les nanotubes de carbone grâce à l'utilisation combinée d'un fort champ magnétique (60T) et d'un contrôle électrostatique du dopage électronique. Il s'agit alors de montrer les rôles clés joués par la structure de bande en énergie et par le désordre. Plusieurs types de tubes métalliques de qualité structurale variable ont été étudiés. Selon le rapport entre le libre parcours moyen élastique (le) et la circonférence du nanotube (L), différents régimes apparaissent. Lorsque le>L, une conduction balistique s'installe et met en avant le rôle unique de la structure de bande. Une ouverture complète du gap en énergie sous champ magnétique est observée (effet Aharonov-Bohm, AB). Une modélisation basée sur le formalisme de Landauer rend alors compte du rôle prépondérant des barrières Schottky aux contacts. C'est la première évidence expérimentale de l'effet AB par les modulations des barrières Schottky.This thesis is devoted to the study of the electronic transport in carbon nanotubes. In this scheme, we combine a high magnetic field (60T) with an electrostatic control of the electronic doping. The goal is to show the key role played by the energy band structure and the disorder. Several kind of metallic tubes with variable structural quality have been studied. Depending on the ratio between the elastic mean free path (le) and the nanotube circumference (L), different regimes appear. When le>L, a ballistic conduction is established and clearly shows the unique role of the band structure. A complete opening of the energy gap under magnetic field is observed (Aharonov-Bohm effect, AB). A simulation based on the Landauer formalism explains the prominent role of the Schottky barrier at the contacts. It is the first experimental evidence of the Aharonov-Bohm Schottky barrier modulations.TOULOUSE-INSA (315552106) / SudocSudocFranceF

Coupling Mechanics to Charge Transport in Carbon Nanotube Mechanical Resonators

4 pages, 4 figures.-- Printed version published Aug 28, 2009.-- Supporting information available at: www.sciencemag.org/cgi/content/full/1174290/DC1Nanoelectromechanical resonators have potential applications in sensing, cooling, and mechanical signal processing. An important parameter in these systems is the strength of coupling the resonator motion to charge transport through the device. We investigate the mechanical oscillations of a suspended single-walled carbon nanotube that also acts as a single-electron transistor. The coupling of the mechanical and the charge degrees of freedom is strikingly strong as well as widely tunable (the associated damping rate is ~ 5 · 10^5 Hz). In particular, the coupling is strong enough to drive the oscillations in the nonlinear regime.Peer reviewe

Un transistor à effet de champ à base de nanorubans de graphène avec les bords remplis.

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