Ideal One-dimensional System Research Articles

Tailoring the photophysical properties of carbon nanotubes by photonic nanostructures

Single-walled carbon nanotubes (SWCNTs) are nearly ideal one-dimensional systems with potential applications in a wide range of fields. The rich physics of SWCNTs arise from the excitonic nature of their photophysical properties. This review is focused on the results of novel research activities that explore how the photophysical properties of SWCNTs can be altered via their integration with photonic nanostructures including plasmonic structures and photonic microcavities that have resulted in phenomena such as photocurrent enhancement, selection rule breakdown and photoluminescence (PL) modification.

Fabrication of graphene nanoribbons through mechanical cleavage and their electronic transport properties at low temperature

We have fabricated graphene nanoribbons (GNRs) of length up to tens of microns through mechanical cleavage, and performed electron transport measurements on devices made of the GNRs down to a low temperature of 0.3 K. Fabry-Perot interference was observed in the conductance of the devices as functions of both bias voltage and gate voltage. The result indicates that our mechanically cleaved GNRs are of high quality, in which the electrons form an ideal one-dimensional system at low temperatures.

Friction and Diffusion of Matter-Wave Bright Solitons

We consider the motion of a matter-wave bright soliton under the influence of a cloud of thermal particles. In the ideal one-dimensional system, the scattering process of the quasiparticles with the soliton is reflectionless; however, the quasiparticles acquire a phase shift. In the realistic system of a Bose-Einstein condensate confined in a tight waveguide trap, the transverse degrees of freedom generate an extra nonlinearity in the system which gives rise to finite reflection and leads to dissipative motion of the soliton. We calculate the velocity and temperature-dependent frictional force and diffusion coefficient of a matter-wave bright soliton immersed in a thermal cloud.

Photoemission spectroscopy on single-wall carbon nanotubes

One-dimensional nature of single-wall carbon nanotubes (SWNTs) has been investigated by the photoemission spectroscopy on SWNT samples with different diameters. We successfully observe peak structures that arise from one-dimensional van Hove singularities. The spectral function and the intensity at the Fermi level both exhibit power-law behavior with almost identical exponents, which indicates that the metallic SWNTs are regarded as ideal one-dimensional systems.

Direct observation of Tomonaga-Luttinger-liquid state in carbon nanotubes at low temperatures.

The electronic transport properties of conventional three-dimensional metals are successfully described by Fermi-liquid theory. But when the dimensionality of such a system is reduced to one, the Fermi-liquid state becomes unstable to Coulomb interactions, and the conduction electrons should instead behave according to Tomonaga-Luttinger-liquid (TLL) theory. Such a state reveals itself through interaction-dependent anomalous exponents in the correlation functions, density of states and momentum distribution of the electrons. Metallic single-walled carbon nanotubes (SWNTs) are considered to be ideal one-dimensional systems for realizing TLL states. Indeed, the results of transport measurements on metal-SWNT and SWNT-SWNT junctions have been attributed to the effects of tunnelling into or between TLLs, although there remains some ambiguity in these interpretations. Direct observations of the electronic states in SWNTs are therefore needed to resolve these uncertainties. Here we report angle-integrated photoemission measurements of SWNTs. Our results reveal an oscillation in the pi-electron density of states owing to one-dimensional van Hove singularities, confirming the one-dimensional nature of the valence band. The spectral function and intensities at the Fermi level both exhibit power-law behaviour (with almost identical exponents) in good agreement with theoretical predictions for the TLL state in SWNTs.

Electron intersubband scattering by confined and localized phonons in real quantum wires

The present study deals with electron intersubband scattering in real quantum wire structures. Both the multi-subband structure and confined phonon modes are considered together. The rates of scattering by confined longitudinal-optical (LO) phonons and by surface-optical (SO) phonons are calculated taking into account all possible LO phonon modes as well as all possible electron intersubband transitions. The estimations of transition rates for GaAs/AlAs QWIS have shown that intrasubband electron scattering and most intersubband transitions are due primarily to scattering by confined LO phonons, but in resonant intersubband transitions the contribution of SO phonons may be dominant when the phonon energy is close to the intersubband energy separation. Moreover, electron-SO-phonon scattering might play an important part in low-temperature electron transport because the GaAs-like SO mode is shifted towards lower frequencies compared with that of LO phonons. The energy dependence of the total scattering rate in an ideal quantum wire exhibits multiple sharp peaks related to each intersubband transition. These peaks originate from the resonant nature of the density of states in ideal one-dimensional systems. It is demonstrated that in real quantum wires with variable thickness the resonant peaks broaden or even disappear due to variation of subband energies.

Isotachophoresis (displacement electrophoresis. Transphoresis) Theory : Structure of the ionic species interface

An approximate solution is given for the equations governing the structure of the inter-species ionic interface in discrete sample isotachophoresis (displacement electrophoresis, transphoresis) in an ideal one-dimensional system, in the presence of a common counterion and in the absence of continuous mobility spectrum spacer ampholytes. It is shown that the approximation is reasonably good for values of the Kohlrausch-regulated terminator leader concentration ratio greater than 0.5. The dependence of interface thickness on mobility and concentration ratios is discussed and results are compared to those in previous literature. Interface thickness is found to be inversely proportional to leader voltage gradient.