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Register a new userTransport Properties of Carbon Nanotube C$_{60}$ Peapods
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We measure the conductance of carbon nanotube peapods from room temperature down to 250mK. Our devices show both metallic and semiconducting behavior at room temperature. At the lowest temperatures, we observe single electron effects. Our results suggest that the encapsulated C$_{60}$ molecules do not introduce substantial backscattering for electrons near the Fermi level. This is remarkable given that previous tunneling spectroscopy measurements show that encapsulated C$_{60}$ strongly modifies the electronic structure of a nanotube away from the Fermi level.
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We theoretically studied the electronic and electrical properties of metallic and semiconducting peapods with encapsulated C_{60} (C_{60}@CNT) as a function of the carbon nanotube (CNT) diameter. For exothermic peapods (CNT diameter > 11.8 A), only minor changes, ascribed to a small structural deformation of the nanotube walls, were observed. These include a small electron charge transfer (less than 0.10 electron) from the CNT to the C_{60} molecules and a poor mixing of the C_{60} orbitals with those of the CNT. Decreasing the diameter of the nanotube leads to a modest increase of the charge density located between the C_{60}s. More significant changes are obtained for endothermic peapods (CNT diameter < 11.8 A). We observe a large electron charge transfer from C_{60} to the tube, and a drastic change in electron transport characteristics and electronic structure. These results are discussed in terms of pi-pi interaction and C_{60} symmetry breaking.
Interaction-induced magnetism at the ends of carbon nanotubes is studied theoretically, with a special focus on magnetic anisotropies. Spin-orbit coupling, generally weak in ordinary graphene, is strongly enhanced in nanotubes. In combination with Coulomb interactions, this enhanced spin-orbit coupling gives rise to a super-spin at the ends of carbon nanotubes with an XY anisotropy on the order of 10 mK. Furthermore, it is shown that this anisotropy can be enhanced by more than one order of magnitude via a partial suppression of the super-spin.
While long-theorized, the direct observation of multiple highly dispersive C$_{60}$ valence bands has eluded researchers for more than two decades due to a variety of intrinsic and extrinsic factors. Here we report a realization of multiple highly dispersive (330-520 meV) valence bands in pure thin film C$_{60}$ on a novel substrate--the three-dimensional topological insulator Bi$_{2}$Se$_{3}$--through the use of angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. The effects of this novel substrate reducing C$_{60}$ rotational disorder are discussed. Our results provide important considerations for past and future band structure studies as well as the increasingly popular C$_{60}$ electronic device applications, especially those making use of heterostructures.
A top-gated single wall carbon nanotube is used to define three coupled quantum dots in series between two electrodes. The additional electron number on each quantum dot is controlled by top-gate voltages allowing for current measurements of single, double and triple quantum dot stability diagrams. Simulations using a capacitor model including tunnel coupling between neighboring dots captures the observed behavior with good agreement. Furthermore, anti-crossings between indirectly coupled levels and higher order cotunneling are discussed.
We investigate a tunable two-impurity Kondo system in a strongly correlated carbon nanotube double quantum dot, accessing the full range of charge regimes. In the regime where both dots contain an unpaired electron, the system approaches the two-impurity Kondo model. At zero magnetic field the interdot coupling disrupts the Kondo physics and a local singlet state arises, but we are able to tune the crossover to a Kondo screened phase by application of a magnetic field. All results show good agreement with a numerical renormalization group study of the device.
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