Peierls-type metal-insulator transition in carbon nanostructures (original) (raw)
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Electron-phonon coupling and Peierls transition in metallic carbon nanotubes
Physical Review B, 2000
We reexamine the putative Peierls transition in a (5,5) metallic nanotube. We show that the conduction electrons at the Fermi level do not couple to the longitudinal acoustic phonon but rather to a folded-in graphene zone edge phonon having the proper Kékulé modulation symmetry. The calculation for the mean-field transition temperature gives 15 K, a value comparable to previous estimates. We discuss the significance of this transition temperature.
Phonon spectromicroscopy of carbon nanostructures with atomic resolution
Physical Review Letters, 2004
The vibrational properties of single-wall carbon nanotubes have been probed locally with atomicscale resolution by inelastic electron tunneling spectroscopy with a low-temperature scanning tunneling microscope. The high spatial resolution has allowed the unraveling of changes in the local phonon spectrum related to topological defects. We demonstrated that the radial breathing mode is suppressed within tube segments of lengths below 3 nm, and that in the cap region phonon modes characteristic of the fullerene hemisphere are emerging. Phonon spectromicroscopy should lead to a better understanding of the mechanisms that limit the transport of heat or electrical charge inside nanostructured carbon materials.
Victoria University of Wellington, 2015
This thesis is cited by: 3. Zambrzycki, M. et al. (2021). "Structure and electrical transport properties of carbon nanofibres/carbon nanotubes 3D hierarchical nanocomposites: Impact of the concentration of acetylacetonate catalyst", Ceramics International, 47 (3), 4020-4033. https://doi.org/10.1016/j.ceramint.2020.09.269 2. Αρετή, Θ. Κ. [Areti, T. K.] (2017). Diploma Thesis, Department of Physics, University of Athens. Available at https://pergamos.lib.uoa.gr/uoa/dl/frontend/file/lib/default/data/1702786/theFile 1. Hang, S. (2015). Irradiation-based defect engineering of graphene devices. PhD Thesis, University of Southampton, UK. Available at http://eprints.soton.ac.uk/388184/ Graphene, consisting of a single layer of carbon atoms, is being widely studied for its interesting fundamental physics and potential applications. The presence and extent of disorder play important roles in determining the electronic conduction mechanism of a conducting material. This thesis presents work on data analysis and modelling of electronic transport mechanisms in disordered carbon materials such as graphene. Based on experimental data of conductance of partially disordered graphene as measured by Gómez-Navarro et al., we propose a model of variable-range hopping (VRH) – defined as quantum tunnelling of charge carriers between localized states – consisting of a crossover from the two-dimensional (2D) electric field-assisted, temperature-driven (Pollak-Riess) VRH to 2D electric field-driven (Skhlovskii) VRH. The novelty of our model is that the temperature-dependent and field-dependent regimes of VRH are unified by a smooth crossover where the slopes of the curves equal at a given temperature. We then derive an analytical expression which allows exact numerical calculation of the crossover fields or voltages. We further extend our crossover model to apply to disordered carbon materials of dimensionalities other than two, namely to the 3D self-assembled carbon networks by Govor et al. and quasi-1D highly-doped conducting polymers by Wang et al. Thus we illustrate the wide applicability of our crossover model to disordered carbon materials of various dimensionalities. We further predict, in analogy to the work of Pollak and Riess, a temperature-assisted, field-driven VRH which aims to extend the field-driven expression of Shklovskii to cases wherein the temperatures are increased. We discover that such an expression gives a good fit to the data until certain limits wherein the temperatures are too high or the applied field too low. In such cases the electronic transport mechanism crosses over to Mott VRH, as expected and analogous to our crossover model described in the previous paragraph. The second part of this thesis details a systematic data analysis and modelling of experimental data of conductance of single-wall carbon nanotube (SWNT) networks prepared by several different chemical-vapour deposition (CVD) methods by Ansaldo et al. and Lima et al. Based on our analysis, we identify and categorize the SWNT networks based on their electronic conduction mechanisms, using various theoretical models which are temperature-dependent and field-dependent. The electronic transport mechanisms of the SWNT networks can be classed into either VRH in one- and two-dimensions or fluctuation-assisted tunnelling (FAT, i.e. interrupted metallic conduction), some with additional resistance from scattering by lattice vibrations. Most notably, for a selected network, we find further evidence for our novel VRH crossover model previously described. We further correlate the electronic transport mechanisms with the morphology of each network based on scanning electron microscopy (SEM) images. We find that SWNT networks which consist of very dense tubes show conduction behaviour consistent with the FAT model, in that they retain a finite and significant fraction of room-temperature conductance as temperatures tend toward absolute zero. On the other hand, SWNT networks which are relatively sparser show conduction behaviour consistent with the VRH model, in that conductance tends to zero as temperatures tend toward absolute zero. We complete our analysis by estimating the average hopping distance for SWNT networks exhibiting VRH conduction, and estimate an indication of the strength of barrier energies and quantum tunnelling for SWNT networks exhibiting FAT conduction.
ZA-derived phonons in the Raman spectra of single-walled carbon nanotubes
Carbon, 2017
We report the observation of four Raman modes in individual, aligned single-walled carbon nanotubes, with frequencies between the RBM and D modes, and above the G ± modes. By studying the diameter and excitation-energy dependence, we find that these strongly dispersive and comparatively intense modes share the lowest-frequency helical phonon branch as the origin, which can be derived from the out-of-plane acoustic (ZA) phonon branch of graphene. This ZA phonon is observed due due to a defect-assisted, double-resonant process, similar to the D mode; its twophonon overtones and combinations with transverse optical (TO) phonons do not require defects. Our assignment is supported by a theoretical model based on sixth-nearest neighbour tight-binding and a force-constant approach. We present a complete theoretical evaluation of the diameter and excitation-energy dependence of the ZA, 2ZA, and TO±ZA modes, which fits very well to our experimental results and previous studies of the so-called region of intermediate frequency modes.
Physical Review B, 2002
We consider Peierls instability due to the interaction of electrons with both acoustic and optical phonons in metallic carbon nanotubes, resulting in a static twist in the nanotube lattice below the critical temperature T c . We study lattice excitations, the so-called solitwiston and polartwiston, over the ordered Peierls state for different types of boundary conditions. Furthermore, we calculate the electrical resistivity and find that our theory offers a possible explanation for the observed low-temperature rise in the electrical resistivity of carbon nanotubes.
Physics Letters A, 2003
We theoretically studied the electronic and electrical properties of metallic and semiconducting nanotube peapods with encapsulated C 60 (C 60 @CNT) as a function of the carbon nanotube ͑CNT͒ diameter. For exothermic peapods ͑the CNT diameterϾ11.8 Å͒, 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 electron͒ 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 diameterϽ11.8 Å͒. 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 ofinteraction and C 60 symmetry breaking.
Electron transport and optical properties of carbon nanostructures from first principles
Computer Physics Communications, 2005
Recent developments in ab initio studies of the nonlinear electron transport and optical properties of nanostructures are discussed. As examples of applications, results are presented for carbon atomic wires and single-walled carbon nanotubes. For the carbon atomic wires, strong nonlinearities in the I -V characteristics and conductance are obtained, and the role of interface chemistry and lead composition is demonstrated to be extremely important in determining its transport properties. For singlewalled carbon nanotubes, explicit treatment of many-electron interactions shows that excitonic effects are dominant in these quasi-one dimensional systems and thus essential to explain the observed optical absorption spectra.
Metal-insulator transition in doped single-wall carbon nanotubes
Physical Review B, 2005
We find strong evidence for a metal-insulator ͑MI͒ transition in macroscopic single wall carbon nanotube ͑SWNT͒ conductors. This is revealed by systematic measurements of resistivity and transverse magnetoresistance ͑MR͒ in the ranges 1.9-300 K and 0-9 Tesla, as a function of p-type redox doping. Strongly H 2 SO 4-doped samples exhibit small negative MR, and the resistivity is low and only weakly temperaturedependent. Stepwise dedoping by annealing in vacuum induces a MI transition. Critical behavior is observed near the transition, with ͑T͒ obeying a power-law temperature dependence, ͑T͒ ϰ T −. In the insulating regime ͑high annealing temperatures͒, the ͑T͒ behavior ranges from Mott-like three-dimensional ͑3D͒ variable-range hopping ͑VRH͒, ͑T͒ ϰ exp͓͑T 0 / T͒ −1/4 ͔, to Coulomb-gap ͑CGVRH͒ behavior, ͑T͒ ϰ exp͓͑−T 0 / T͒ −1/2 ͔. Concurrently, MR͑B͒ becomes positive for large B, exhibiting a minimum at magnetic field B min. The temperature dependence of B min can be characterized by B min ͑T͒ = B c ͑1−T / T c ͒ for a large number of samples prepared by different methods. Below a sample-dependent crossover temperature T c , MR͑B͒ is positive for all B. The observed changes in transport properties are explained by the effect of doping on semiconducting SWNTs and tube-tube coupling.
Conductivity and atomic structure of isolated multiwalled carbon nanotubes
Europhysics Letters (EPL), 1998
We report associated high-resolution transmission electron microscopy (HRTEM) and transport measurements on a series of isolated multiwalled carbon nanotubes. HRTEM observations, by revealing relevant structural features of the tubes, shed some light on the variety of observed transport behaviors, from semiconducting to quasi-metallic type. Non-Ohmic behavior is observed for certain samples which exhibit "bamboo-like" structural defects. The resistance of the most conducting sample exhibits a pronounced maximum at 0.6 K and strong positive magnetoresistance.
Physical Review B, 2006
The electronic band structure, electron-phonon interaction, and superconducting transition are investigated for the ͑5,5͒, ͑10,10͒ armchair and ͑5,0͒ zigzag single walled carbon nanotubes ͑SWCNT͒. While the electronphonon interaction and superconducting transition temperature are very small in ͑5,5͒ and negligibly small in ͑10,10͒ armchair tubes, they are considerable in the ͑5,0͒ zigzag tube. The ͑5,0͒ tube, which is a semiconductor with -bands alone contributing to the band structure, exhibits metallic character withbands hybridization. As a result the van Hove like singularity in the density of states moves towards the top of the valance band enhancing the effective density of states near the Fermi energy. Consequently the electron-phonon interaction increases and the ͑5,0͒ tube turns out to be a superconductor with appreciable transition temperature and found to be the most probable member of the family of 4 Å diameter carbon nanotubes for which the superconducting transition temperature is experimentally measured.