We report a first principles analysis of electronic transport characteristics for (n,n) carbon nanotube bundles. When n is not a multiple of 3, inter-tube coupling causes universal conductance suppression near Fermi level regardless of the rotational arrangement of individual tubes. However, when n is a multiple of 3, the bundles exhibit a diversified conductance dependence on the orientation details of the constituent tubes. The total energy of the bundle is also sensitive to the orientation arrangement only when n is a multiple of 3. All the transport properties and band structures can be well understood from the symmetry consideration of whether the rotational symmetry of the individual tubes is commensurate with that of the bundle.
Using a scattering technique based on a parametrized linear combination of atomic orbitals Hamiltonian, we calculate the ballistic quantum conductance of multi-wall carbon nanotubes. We find that inter-wall interactions not only block some of the quantum conductance channels, but also redistribute the current non-uniformly over the individual tubes across the structure. Our results provide a natural explanation for the unexpected integer and non-integer conductance values reported for multi-wall nanotubes in Ref.[S. Frank, P. Poncharal, Z.L. Wang, and W. A. de Heer, Science 280, 1744 (1998)]
Effect of contact interfaces, between metallic single-wall carbon nanotubes (SWCNT) and external electrodes made also of nanotubes, on the electrical conductance is studied. A tight-binding model with both diagonal and off-diagonal disorder, a recursive Green function technique as well as the Landauer formalism are used. The studies are carried out within the coherent transport regime and are focused on: (i) evolution from conductance quantization to resonant tunneling, (ii) SWCNT's length effects and (iii) magnetoresistance. It is shown that the so-called on-resonance devices, i.e. nanotubes …
We investigate the effects of impurity scattering on the conductance of metallic carbon nanotubes as a function of the relative separation of the impurities. First we compute the conductance of a clean (6,6) tube, and the effect of model gold contacts on this conductance. Then, we compute the effect of introducing a single, two, and three oxygen atom impurities. We find that the conductance of a single-oxygen-doped (6,6) nanotube decreases by about 30 % with respect to that of the perfect nanotube. The presence of a second doping atom induces strong changes of the conductance which, however, d…
We use DFT to study the effect of molecular adsorbates on the conductance of metallic carbon nanotubes. The five molecules considered (NO2, NH2, H, COOH, OH) lead to similar scattering of the electrons. The adsorption of a single molecule suppresses one of the two available channels of the CNT at low bias conductance. If more molecules are adsorbed on the same sublattice, the remaining open channel can be blocked or not, depending on the relative position of the adsorbates. If a simple geometric condition is fulfilled this channel is still open, even after adsorbing an arbitrary number of mole…
We present a first-principles study of the electronic transport properties of micrometer long semiconducting CNTs randomly covered with carbene functional groups. Whereas prior studies suggested that metallic tubes are hardly affected by such addends, we show here that the conductance of semiconducting tubes with standard diameter is on the contrary severely damaged. The configurational averaged conductance as a function of tube diameter and with a coverage of up to one hundred functional groups is extracted. Our results indicate that the search for a conductance-preserving covalent functional…
We measure electrical transport on networks of single wall nanotube ropes as a function of temperature T, voltage V and pressure up to 22GPa. We observe Luttinger liquid (LL) behavior, a conductance ~T^alpha and a dynamic conductance ~V^alpha. With pressure conductance increases while alpha decreases, enabling us to test the theoretical prediction for LL on the alpha dependence of the T and V independent coefficient of the tunneling conductance, and to obtain the high frequency cut-off of LL modes. The possible transition to a fermi liquid at alpha -> 0 is unattainable, as nanotubes collapse t…
Quantum interference has dramatic effects on electronic transport through nanotube contacts. In optimal configuration the intertube conductance can approach that of a perfect nanotube ($4e^2/h$). The maximum conductance increases rapidly with the contact length up to 10 nm, beyond which it exhibits long wavelength oscillations. This is attributed to the resonant cavity-like interference phenomena in the contact region. For two concentric nanotubes symmetry breaking reduces the maximum intertube conductance from $4e^2/h$ to $2e^2/h$. The phenomena discussed here can serve as a foundation for bu…
We study the influence of structural lattice fluctuations on the elastic electron transport in single-wall carbon nanotubes within a density-functional-based scheme. In the linear response regime, the linear conductance is calculated via configurational averages over the distorted lattice. Results obtained from a frozen-phonon approach as well as from molecular dynamics simulations are compared. We further suggest that the effect of structural fluctuations can be qualitatively captured by the Anderson model with bond disorder. The influence of individual vibrational modes on the electronic tra…
We have calculated the effects of structural distortions of armchair carbon nanotubes on their electrical transport properties. We found that the bending of the nanotubes decreases their transmission function in certain energy ranges and leads to an increased electrical resistance. Electronic structure calculations show that these energy ranges contain localized states with significant $σ$-$π$ hybridization resulting from the increased curvature produced by bending. Our calculations of the contact resistance show that the large contact resistances observed for SWNTs are likely due to the weak …
Analytic results for the conductance of a molecular wire attached to mesoscopic tubule leads are obtained. They permit to study linear transport in presence of low dimensional leads in the whole range of parameters. In particular contact effects can be addressed in detail. By focusing on the specificity of the lead-wire contact, we show that the geometry of this hybrid system supports a mechanism of channel selection, which is a distinctive hallmark of the mesoscopic nature of the electrodes.
We propose a nonequilibrium Green's function approach to calculate the ac conductance of various finite-length carbon nanotubes. The simulated ac conductance differs significantly from that of the infinite-length ones. At the low-frequency limit, the profiles of the quantized conductance are still observable in the finite-length carbon nanotubes, but many more peaks appear on the conductance curves. We also show that the conductance of finite-length carbon nanotubes will oscillate as a function of the ac frequency. The dependence of the oscillation on the lengths, helicities and defects of the…
We investigate thermal energy coupling between carbon nanotubes (CNTs) and SiO2 with non-equilibrium molecular dynamics simulations. The thermal boundary conductance (g) per unit CNT length is found to scale proportionally with the strength of the Van der Waals interaction (~X), with CNT diameter (~D), and as a weak power law of temperature (~T^1/3 between 200-600 K). The thermal relaxation time of a single CNT on SiO2 is independent of diameter, tau ~ 85 ps. With the standard set of parameters g ~ 0.1 W/m/K for a 1.7 nm diameter CNT at room temperature. Our results are comparable to, and expl…
Vertically aligned ZnO nanotube arrays fabricated on an ITO substrate are found to exhibit strong persistent photoconductivity (PPC) effect and electrically driven conductance switching behavior, though the latter shows a gradual decay from high conductance state to a low conductance state. Unlike the electrical switching, the PPC cannot be reset or reversed by an electrical pulse. Excitation wavelength dependent conductance measurement indicates the presence of the defect localized states (DLS) ~ 240meV above the valence band edge, in support of the hypothesis that the doubly ionization of th…
The thermal properties of a suspended metallic single-wall carbon nanotube (SWNT) are extracted from its high-bias (I-V) electrical characteristics over the 300-800 K temperature range, achieved by Joule self-heating. The thermal conductance is approximately 2.4 nW/K and the thermal conductivity is nearly 3500 W/m/K at room temperature for a SWNT of length 2.6 um and diameter 1.7 nm. A subtle decrease in thermal conductivity steeper than 1/T is observed at the upper end of the temperature range, which is attributed to second order three-phonon scattering between two acoustic modes and one opti…
The heat flux autocorrelation functions of carbon nanotubes (CNTs) with different radius and lengths is calculated using equilibrium molecular dynamics. The thermal conductance of CNTs is also calculated using the Green-Kubo relation from the linear response theory. By pointing out the ambiguity in the cross section definition of single wall CNTs, we use the thermal conductance instead of conductivity in calculations and discussions. We find that the thermal conductance of CNTs diverges with the CNT length. After the analysis of vibrational density of states, it can be concluded that more low …
The current carrying capacity of ballistic electrons in carbon nanotubes that are coupled to ideal contacts is analyzed. At small applied voltages, where electrons are injected only into crossing subbands, the differential conductance is $4e^2/h$. At applied voltages larger than $ΔE_{NC}/2e$ ($ΔE_{NC}$ is the energy level spacing of first non crossing subbands), electrons are injected into non crossing subbands. The contribution of these electrons to current is determined by the competing processes of Bragg reflection and Zener type inter subband tunneling. In small diameter nanotubes, Bragg r…
Jeong-O Lee et al. [Phy. Rev. B, 61, R16 362 (2000)] reported magnetoresistance and differential conductance measurements of multiwalled carbon nanotubes. The observed aperiodic conductance fluctuations and the negative magnetoresistance was interpreted to originate exclusively from changes in the density of states at the Fermi energy. We show that this interpretation is questionable and not supported by their measurements.
We address the electronic resonant transport in presence of a transverse magnetic field through the single level of a suspended carbon nanotube acting as a quantum oscillator. We predict a negative magneto-conductance with a magnetic-field induced narrowing of the resonance line and a reduction of the conductance peak when the nanotube is asymmetrically contacted to the leads. At finite bias voltage we study the threshold for phonon-assisted transport.
By introducing a normal self-energy to incorporate the effects of magnetic impurities, Kondo effects in single-walled metallic carbon nanotubes are investigated within the Anderson model and Landauer formula. Magnetic impurities induce Kondo resonance and bring a valley of conductance unction near the Fermi level. The conductance of the nanotube increases with the temperature in the low temperature range. Thermoelectric power induced by magnetic impurities is gotten from Mott relation, and the calculations indicate its dependence on the temperature could interpret the experiment well.
We use the energy analysis as a perturbative method to study the effect of electron-radial breathing mode (RBM) phonon interaction on the electrical conductivity of long metallic zigzag carbon nanotubes (CNTs). The band structure of zigzag CNTs is calculated by exerting zone-folding method on relations derived by using the nearest neighbor approximation of tight-binding expression for the $π$ valence and conduction bands of graphene. The small hollow cylinder model, with two different approximations, is used to obtain the RBM frequency in our calculation. As the result, we have calculated the …
We report the realization and characterization of independently controllable tunnel barriers within a carbon nanotube. The nanotubes are mechanically bent or kinked using an atomic force microscope, and top gates are subsequently placed near each kink. Transport measurements indicate that the kinks form gate-controlled tunnel barriers, and that gates placed away from the kinks have little or no effect on conductance. The overall conductance of the nanotube can be controlled by tuning the transmissions of either the kinks or the metal-nanotube contacts.
A new form of gold nanobridges has been recently observed in ultrahigh-vacuum experiments, where the gold atoms rearrange to build helical nanotubes, akin in some respects to carbon nanotubes. The good reproducibility of these wires and their unexpected stability will allow for conductance measurements and make them promising candidates for future applications . We present here a study of the transport properties of these nanotubes in order to understand the role of chirality and of the different orbitals in quantum transport observables. The conductance per atomic row shows a light decreasing…
Motivated by recent experiments on electronic transport through a carbon nanotube, we investigate the role of the intra- and inter-orbital Coulomb interactions on the temperature evolution of the conductance. It is shown that small amount (~10%) of asymmetry between these Coulomb repulsions substantially deforms the conductance profile at finite temperature, particularly around half-filling. The nature of such thermal symmetry crossover is elucidated.
We have prepared solutions of multiwalled carbon nanotubes in Aroclor 1254, a mixture of polychlorinated biphenyls. The solutions are stable at room temperature. Transport measurements were performed using a scanning--tunneling probe on a sample prepared by spin--coating of the solution on gold substrates. Conductance steps were clearly seen. An histogram of a high number of traces shows maximum peaks at integer values of the conductance quantum $G_0 = 2e^2/h$, demonstrating ballistic transport at room temperature along the carbon nanotube over distances longer than $1.4μm$.
We investigate transport through a single impurity in metallic zigzag carbon nanotube and find the conductance sensitively depends on the impurity strength and the bias voltage. It is rather interesting that interplay between the current-carrying scattering state and evanescent modes leads to rich phenomena including resonant backward scattering, perfect tunneling and charge accumulations. In addition, we also find a dual relation between the backscattered conductance and the charge accumulation. At the end, relevance to the experiments is discussed.
The interaction and tunneling conductance between oppositely located ends of coaxial carbon nanotubes are studied by the example of two (11,11) nanotubes with open ends terminated by hydrogen atoms. The Green function formalism is applied to determine the tunneling current through the nanotube ends as a function of the distance between the ends, relative orientation of the nanotubes and voltage applied. The energy favorable configuration of the coaxial nanotubes is obtained by the analysis of their interaction energy at different distances between the nanotube ends and angles of their relative…
Explicit expressions of the band spectrum near the neutrality point for armchair and zigzag graphene ribbons and carbon nanotubes were derived based on a tight-binding macromolecule model of graphene. The obtained dispersion relations are used to determine and compare the conductance ladders of these structures and are beneficial for many other applications. Our results are different in many respects from previously reported data. This new information forms a solid reliable basis for evaluation of the potential of graphene nanoelectronic devices.
We present an approach for time-dependent quantum transport based on a self-consistent non-equilibrium Green function formalism. The technique is applied to a ballistic carbon nanotube transistor in the presence of a time harmonic signal at the gate. In the ON state the dynamic conductance exhibits plasmonic resonant peaks at terahertz frequencies. These vanish in the OFF state, and the dynamic conductance displays smooth oscillations, a signature of single particle quantum effects. We show that the nanotube kinetic inductance plays an essential role in the high-frequency behavior.
Using the Landauer-Buttiker formalism, we calculate the effect of structural twist on electron transport in conducting carbon nanotubes. We demonstrate that even a localized region of twist scatters the propagating pi electrons and induces the opening of a (pseudo-) gap near the Fermi level. The subsequent conductance reduction may be compensated by an applied axial magnetic field, leading to a twist-induced, giant positive magneto-conductance in clean armchair nanotubes.
We present a mechanism to improve the conductivity of carbon nanotube (CNT) networks by improving the conductance between CNTs of different chirality. We argue generally that a weak perturbation can greatly improve the inter-tube conductance by allowing momentum-conserving tunnelling. The mechanism is verified with a tight-binding model, allowing an investigation of its impact for a network containing a range of chiralities. We discuss practical implementations, and conclude that it may be effected by weak physical interactions, and therefore does not require chemical bonding to the CNTs.
The electron transport through the nanotube junctions which connect the different metallic nanotubes by a pair of a pentagonal defect and a heptagonal defect is investigated by Landauer's formula and the effective mass approximation. From our previous calculations based on the tight binding model, it has been known that the conductance is determined almost only by two parameters,i.e., the energy in the unit of the onset energy of more than two channels and the ratio of the radii of the two nanotubes. The conductance is calculated again by the effective mass theory in this paper and a simple an…
We report on our theoretical study of the magnetoresistance in spin polarized transport through a finite carbon nanotube (CNT). Varying the Fermi energy of a CNT and the relative strength of couplings to two ferromagnetic (FM) electrodes, we studied the conductance as well as the magnetoresistance (MR). Due to resonant transport through discrete energy levels in a finite CNT, the conductance and MR are oscillating as a function of the CNT Fermi energy. The MR is peaked at the conductance valleys and dipped close to the conductance peaks. When couplings to two FM electrodes are asymmetric, the …
Inter-tube conductance of double-wall carbon nanotubes with impurities is numerically studied. Its length dependence for various impurities is scaled by a mean-free path. The inter-tube conductance exhibits drastic linear increase with the tube length and takes a maximum around at the localization length. The maximum conductance is much smaller than the conductance quantum $e^2/π\hbar$.
We discuss the conductance of a molecular bridge between mesoscopic electrodes supporting low-dimensional transport and bearing an internal structure. As an example for such nanoelectrodes we assume semi-infinite (carbon) nanotubes. In the Landauer scattering matrix approach, we show that the conductance of this hybrid is very sensitive to the geometry of the contact unlike the usual behaviour in the presence of bulk electrodes.
Linear transport through a single-walled carbon nanotube ring (CNR), pierced by a magnetic field and capacitively coupled to a gate voltage source, is investigated starting from a model of interacting $p_z$-electrons. The dc-conductance, calculated in the limit of weak tunneling between the ring and the leads, displays a periodic resonance pattern determined by the interplay between Coulomb interactions and quantum interference phenomena. Coulomb blockade effects are manifested in the absence of resonances for any applied flux in some gate voltage regions; the periodicity as a function of the …
Through magnetic linear dichroism spectroscopy, the magnetic susceptibility anisotropy of metallic single-walled carbon nanotubes has been extracted and found to be 2-4 times greater than values for semiconducting single-walled carbon nanotubes. This large anisotropy is consistent with our calculations and can be understood in terms of large orbital paramagnetism of electrons in metallic nanotubes arising from the Aharonov-Bohm-phase-induced gap opening in a parallel field. We also compare our values with previous work for semiconducting nanotubes, which confirm a break from the prediction tha…
We present first-principles calculations of quantum transport which show that the resistance of metallic carbon nanotubes can be changed dramatically with homogeneous transverse electric fields if the nanotubes have impurities or defects. The change of the resistance is predicted to range over more than two orders of magnitude with experimentally attainable electric fields. This novel property has its origin that backscattering of conduction electrons by impurities or defects in the nanotubes is strongly dependent on the strength and/or direction of the applied electric fields. We expect this …
We compute electrostatic fields induced deformations of cantilevered finite-length metallic carbon nanotubes, using an energy minimization method based on a charge-dipole moment interaction potential combined with an empirical many-body potential. The influence of field strength, field direction and tube geometry on the electrostatic deflection is investigated for both single and double walled tubes. These results could apply to nanoelectromechanical devices based on cantilevered carbon nanotubes.
We proposed a new way, adding intertube atoms, to enhance interfacial thermal conductance (ITC) between SiC-carbon nanotube (CNT) array structure. Non-equilibrium molecular dynamics method was used to study the ITC. The results show that the intertube atoms can significantly enhance the ITC. The dependence of ITC on both the temperature and the number of intertube atoms are shown. The mechanism is analyzed by calculating probability distributions of atomic forces and vibrational density of states. Our study may provide some guidance on enhancing the ITC of CNT-based composites.
Conductance measurements of carbon nanotubes containing gated local depletion regions exhibit plateaus as a function of gate voltage, spaced by approximately e2/h, the quantum of conductance for a single (non-degenerate) mode. Plateau structure is investigated as a function of bias voltage, temperature, and magnetic field. We speculate on the origin of this surprising quantization, which appears to lack band and spin degeneracy.
In a telescoped double-walled nanotube (TDWNT), with the inner tube partially extracted from the outer tube, the total current is forced to flow between the layers. Considering the interlayer Hamiltonian as a perturbation, we can obtain an analytic formula for the interlayer conductance. The accuracy of the perturbation formula is systematically improved by including higher-order terms. The interlayer interaction effective in the perturbation formula is the product of the interlayer Hamiltonian and the wave function. It clarifies the effects of the spatial range of the interlayer Hamiltonian a…
Low-dimensional metallic transport is at the heart of modern high-performance transistors. While the best devices are currently based on III-V heterojunction quantum-well channels, we demonstrate that much greater performance gains reside in the unique properties of one-dimensional carbon nanotubes. Using recent experimental data, we show how the specific features of degenerate carrier kinetics in metallic nanotubes enable a novel class of quantum-confined signal detector whose current gain exceeds present transistor technology. We analyze the key interplay of degeneracy and scattering dynamic…
The random phase approximation (RPA) theory is used to derive the Luttinger parameter g for metallic carbon nanotubes. The results are consistent with the Tomonaga-Luttinger models. All metallic carbon nanotubes, regardless if they are armchair tubes, zigzag tubes, or chiral tubes, should have the same Luttinger parameter g. However, a (10,10) carbon peapod should have a smaller g value than a (10,10) carbon nanotube. Changing the Fermi level by applying a gate voltage has only a second order effect on the g value. RPA theory is a valid approach to calculate plasmon energy in carbon nanotube s…
Freely suspended metallic single-wall carbon nanotubes (SWNTs) exhibit reduced current carrying ability compared to those lying on substrates, and striking negative differential conductance (NDC) at low electric fields. Theoretical analysis reveals significant self-heating effects including electron scattering by hot non-equilibrium optical phonons. Electron transport characteristics under strong self-heating are exploited for the first time to probe the thermal conductivity of individual SWNTs (~ 3600 Wm-1K-1 at T=300 K) up to ~700 K, and reveal a 1/T dependence expected for Umklapp phonon sc…
The appearance of a broad peak at $\sim$1550 cm$^{-1}$ (G$^{-}$ peak) in carbon nanotube resonant Raman scattering spectra has been conventionally attributed to the presence of metallic nanotubes. Here, we present resonant Raman measurements on macroscopic nanotube ensembles enriched in armchair species prepared through density gradient ultracentrifugation. Our data clearly demonstrate that the broad G$^{-}$ mode is absent for armchair structures and appears only when the excitation laser is resonant with non-armchair "metals." Due to the large number ($\sim$10$^{10}$) of nanotubes across seve…
We present numerical renormalization group calculations for the zero-bias conductance of quantum dots made from semiconducting carbon nanotubes. These explain and reproduce the thermal evolution of the conductance for different groups of orbitals, as the dot-lead tunnel coupling is varied and the system evolves from correlated Kondo behavior to more weakly correlated regimes. For integer fillings $N=1,2,3$ of an SU(4) model, we find universal scaling behavior of the conductance that is distinct from the standard SU(2) universal conductance, and concurs quantitatively with experiment. Our resul…
We study the electrical transport properties of well-contacted ballistic single-walled carbon nanotubes in a three-terminal configuration at low temperatures. We observe signatures of strong electron-electron interactions: the conductance exhibits bias-voltage-dependent amplitudes of quantum interference oscillation, and both the current noise and Fano factor manifest bias-voltage-dependent power-law scalings. We analyze our data within the Tomonaga-Luttinger liquid model using the non-equilibrium Keldysh formalism and find qualitative and quantitative agreement between experiment and theory.
Electron scattering rates in metallic single-walled carbon nanotubes are studied using an atomic force microscope as an electrical probe. From the scaling of the resistance of the same nanotube with length in the low and high bias regimes, the mean free paths for both regimes are inferred. The observed scattering rates are consistent with calculations for acoustic phonon scattering at low biases and zone boundary/optical phonon scattering at high biases.
As a novel function of ferromagnet (FM)/spacer/FM junctions, we theoretically investigate multiple-valued (or multi-level) cell property, which is in principle realized by sensing conductances of four states recorded with magnetization configurations of two FMs; (up,up), (up,down), (down,up), (down,down). In order to sense all the states, 4-valued conductances corresponding to the respective states are necessary. We previously proposed that 4-valued conductances are obtained in FM1/spin-polarized spacer (SPS)/FM2 junctions, where FM1 and FM2 have different spin polarizations, and the spacer de…
Using a perturbative approach, the effects of the energy gap induced by the Aharonov-Bohm (AB) flux on the transport properties of defective metallic single-walled carbon nanotubes (MSWCNTs) are investigated. The electronic waves scattered back and forth by a pair of impurities give rise to Fabry-Perot oscillations which constitutes a coherent backscattering interference pattern (CBSIP). It is shown that, the CBSIP is aperiodically modulated by applying a magnetic field parallel to the nanotube axis. In fact, the AB-flux brings this CBSIP under control by an additional phase shift. As a conseq…
We report electrical transport experiments using the phenomenon of electrical breakdown to perform thermometry that probe the thermal properties of individual multi-walled nanotubes. Our results show that nanotubes can readily conduct heat by ballistic phonon propagation, reaching a quantum-mechanical limit to thermal conductance. We determine the thermal conductance quantum, the ultimate limit to thermal conductance for a single phonon channel, and find good agreement with theoretical calculations. Moreover, our results suggest a breakdown mechanism of thermally activated C-C bond breaking co…
The dependence of the interwall conductance on distance between walls and relative positions of walls are calculated at the low voltage by Bardeen method for (n,n)@(2n,2n) double-walled carbon nanotubes (DWCNTs) with n = 5, 6, ..., 10. The calculations show that interwall conductance does not depend on temperature (for T < 500 K) and current-voltage characteristic is linear. The conductance decreases by 6 orders of magnitude when the interwall distance is doubled. Thus, depending on the interwall distance, DWCNTs can be used as temperature stable nanoresistors or nanocapacitors.
The electron transport in a four-terminal nanodevice consisting of two crossed nanotubes is investigated in the framework of the Landauer-Buttiker formalism. The evident formula for the ballistic conductance of the device is found using a model of crossed conductive cylinders with a point contact between them. Sharp conductance dips stipulated by resonance scattering on the contact are shown to appear in the conductance of the first cylinder. The conductance between the cylinders has resonant behavior. The form and the position of resonant peaks are studied. Our results indicate that the form …
We measure the small signal, 1 GHz source-drain dynamical conductance of a back-gated single-walled carbon nanotube field effect transistor at both low and high dc bias voltages. At all bias voltages, the intrinsic device dynamical conductance at 1 GHz is identical to the low frequency dynamical conductance, consistent with the prediction of a cutoff frequency much higher than 1 GHz. This work represents a significant step towards a full characterization of a nanotube transistor for RF and microwave amplifiers.
We have explored the low-temperature linear and non-linear electrical conductance $G$ of metallic carbon nanotubes (CNTs), which were grown by the chemical-vapor deposition method. The high transparency of the contacts allows to study these two-terminal devices in the high conductance regime. We observe the expected four-fold shell pattern together with Kondo physics at intermediate transparency {$G\alt 2e^2/h$} and a transition to the open regime in which the maximum conductance is doubled and bound by $G_{max}=4e^2/h$. In the high-$G$ regime, at the transition from a quantum dot to a weak li…
Fano resonance spectra for the G band in metallic carbon nanotubes are calculated as a function of laser excitation energy in which the origin of the resonance is given by an interference between the continuous electronic Raman spectra and the discrete phonon spectra. We found that the second-order scattering process of the non-zero q electron-electron interaction is more relevant to the continuous spectra rather than the q = 0 first-order process because the q = 0 direct Coulomb interaction vanishes due to the symmetry of the two sublattices of a nanotube. We also show that the RBM spectra of…
We investigate the molecular sensing properties of carbon nanotube-boron nitride-carbon nanotube (CNT-BN-CNT) junctions. We demonstrate that the electrical conductance of such a junction changes in response to the binding of an analyte molecule to the region of BN. The change in conductance depends on the length of the BN spacer and the position of the analyte and therefore we propose a method of statistically analysing conductance data. We demonstrate the ability to discriminate between analytes, by computing the conductance changes due to three analytes (benzene, thiol-capped oligoyne and a …
We investigate the quantum transport through a single-wall carbon nanotube connected to leads in the presence of an external radiation field. We analyze the conductance spectrum as a function of the frequency and strength of the field. We found that above a critical value of the field intensity, an enhancement of the conductance, or suppressed resistance, as a function of the field strength occurs. The conductance increases displaying oscillations which amplitude shows a strong dependence on the field frequency. For low radiation energies in comparison to the lead-CNT coupling energies, the os…
In ferromagnetic nanostructures, the ballistic anisotropic magnetoresistance (BAMR) is a change in the ballistic conductance with the direction of magnetization due to spin-orbit interaction. Very recently, a directional dependent ballistic conductance has been predicted to occur in a number of newly synthesized nonmagnetic semiconducting nanostructures subject to externally applied magnetic fields, without necessitating spin-orbit coupling. In this article, we review past works on the prediction of this BAMR effect in core-shell nanowires and rolled-up nanotubes. This is complemented by new r…
Devices formed from single molecules attached to noble-metal electrodes exhibit large conductance fluctuations, which inhibit their development as reproducible functional units. We demonstrate that single molecules with planar anchor groups attached to carbon-based electrodes are more resilient to atomic-scale variation in the contacts and exhibit significantly lower conductance fluctuations. We examine the conductance of a 2,6-dibenzylamino core-substituted naphthalenediimide chromophore attached to carbon electrodes by either phenanthrene anchors or more extended anchor groups, which include…
