International Journal of Modern Physics B

We present an overview of strong correlations in single-wall carbon nanotubes, and an introduction to the techniques used to study them theoretically. We concentrate on zigzag nanotubes, although universality dictates that much of the theory can also be applied to armchair or chiral nanotubes. We show how interaction effects lead to exotic low energy properties and discuss future directions for studies on correlation effects in nanotubes.

We study generic effects on the quantum dynamics of classical trapping-leaking mechanism by investigating in detail the 2δ-kicked rotors whose classical phase space is partitioned into momentum cells separated by trapping regions which slow down the motion. We focus on a range of parameters where the dynamics is generic, namely, the phase space has no stable islands. As a consequence of the trapping-leaking mechanism, we show that the classical motion is described by a process of anomalous diffusion. We investigate in detail the impact of the underlying classical anomalous diffusion on the quantum dynamics with special emphasis on the phenomenon of dynamical localization. Based on the study of the quantum density of probability, its second moment and the return probability, we identify a region of weak dynamical localization where the quantum diffusion is still anomalous but the diffusion rate is slower than in the classical case. Moreover, we examine how other relevant time scales, such as the quantum-classical breaking time and the one related to the beginning of full dynamical localization, are modified by the classical anomalous diffusion. Finally, we discuss the relevance of our results for understanding the role of classical cantori in quantum mechanics.

Zn_1-xCr_xO(x = 0, 0.03, 0.09) films were prepared by the radio frequency (RF) magnetron sputtering technique on Si(111) and quartz glass substrates. The effects of Cr-doping on the structural and optical properties of ZnO films have been discussed. The structural properties were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM) while optical properties using UV-Visible spectrophotometer (UV-VIS). XRD measurement revealed that the films were single phase and wurtzite structure with c-axis orientation. With the increase of Cr concentration, the intensity of the (002) peak and the grain size of the Zn_1-xCr_xO(x = 0, 0.03, 0.09) films decreased, and the Full Width at Half Maximum (FWHM) of (002) peak, the crystal lattice parameter c of Zn_1-xCr_xO(x = 0, 0.03, 0.09) films and the width of optical band gap increased, respectively. In the transmittance spectra of the Zn_1-x Cr_xO(x = 0, 0.03, 0.09) films, the movement of the absorption edge of the ultraviolet region is the Burstein–Moss shift with the increase of Cr concentration.

An ensemble Monte Carlo simulation is used to compare bulk electron ballistic transport in 6H-SiC and GaN materials. Electronic states within the conduction band valleys at Γ₁, U, M, Γ₃, and K are represented by nonparabolic ellipsoidal valleys centered on important symmetry points of the Brillouin zone. The large optical phonon energy (~120 meV) and the large intervalley energy separation between the Γ and satellite conduction band valleys suggest an increasing role for ballistic electron effects in 6H-SiC, especially when compared with most III-V semiconductors such as GaAs. Transient velocity overshoot has been simulated, with the sudden application of fields up to ~5×10⁷Vm^-1, appropriate to the gate-drain fields expected within an operational field effect transistor.

A peak-saturation drift velocity ratio of 2:1 is predicted for 6H-SiC material while that for GaN is 4:1. The electron drift velocity relaxes to the saturation value of ~2×10⁵ms^-1 within 3 ps, for both crystal structures. The transient velocity overshoot characteristics are in fair agreement with other recent calculations.

A minimal model for the description of cuprate superconductor characteristics on doping scale (hole and electron) is developed. The leading interband pairing channel couples an itinerant band and defect states created by doping. Bare gaps between them are supposed and become closed by extended doping. Band overlap conditions determine special points in the phase diagram. Nodal and antinodal momentum regions are distinguished. Illustrative calculations have been made using a mean-field pair-transfer multiband Hamiltonian and corresponding free-energy expansions. The results are self-consistent and demonstrate that the elaborated approach is able to reproduce characteristic features of cuprate superconductors as, e.g., the doping dependence of T_c, superconducting gaps and pseudogaps, supercarrier density and effective mass, coherence length and penetration depth, critical magnetic fields and some other properties. Interband pairing scheme is suggested to be an essential aspect of cuprate superconductivity.

The relation between current density and mass density in the plasma has been derived based on the assumption that the magnetic entropy is constant in time. Over the entire range of quasi-stationary ohmic conditions, it is obtained . Here j₀ and ρ₀ are the central values of j and ρ with j₀ ≈ cB/2πR₀ (this corresponds to a value q ≈ 1 of the safety factor near the minor axis).

Historically, the development of equations of state for fluids has almost invariably followed the lead of the van der Waals (vdW) equation which includes an attraction term and a repulsion term. In this paper, using a simple statistical mechanics model, we introduce a parameter σ as both the power and a coefficient of the packing fraction y which locates at the numerator of the vdW attraction term. Then nine equations of state are constructed to solve the critical conditions and the main thermodynamic properties of pure substances at liquid-vapor equilibrium. As a result, the correct critical compressibility factors of Nitrogen, Argon, Carbon dioxide, Ethene, Methane, Oxygen, Propene, Water and Hydrogen, are obtained with an optimal choice of parameter σ. Good predictions of these equations to the liquid-vapor equilibrium properties below critical temperature are reported and compared with experimental data.

The aim of this paper is to provide validity and reliable analytical relation for the thermodynamic functions calculated in terms of the Debye temperature using incomplete gamma functions, and examines the entropy and specific heat capacity of hexagonal single crystals of GaN in the 0–1800 K temperature range. The obtained results have been compared with the corresponding experimental and theoretical results. Our results are in excellent agreement with the theoretical results over the entire temperature range. It has also shown that at low temperature, our results are in very good agreement with the experimental results, however, at high temperature, our results are lower than other experimental results.

This work presents the study of the effect of trap states at the oxide-silicon interface in lightly doped polycrystalline silicon thin-film transistors with large grains. In this study, it is assumed that the oxide-silicon interface traps are evenly distributed throughout the interface region and single grain boundary is present in the channel of poly-Si TFT. It is shown that improved device characteristics can be obtained by reducing the gate oxide thickness. It is also observed that as gate oxide thickness decreases for a constant value of trap state density in the oxide-silicon interface, the gate voltage required for channel formation is lowered and leads to a decrease in threshold voltage of the device. Calculated and experimental results are also found to be well consistent with each other.

We study stochastic resonance (SR) in Hindmarsh–Rose (HR) neural network with small-world (SW) connections driven by external periodic stimulus, focusing on the dependence of properties of SR on the network structure parameters. It is found that, the SW neural network enhances SR compared with single neuron. By turning coupling strength c, two categories of SR were gained. With the connection-rewiring probability p increasing, the resonance curve becomes more and more sharp and the peak value increases gradually and then reaches saturation. The SW network enhances the SR peak value compared with regular network and widens resonance in ascending range compared with random network. When decreasing node degree k, the resonance range is enlarged, and the signal noise ratio (SNR) curve becomes a two peak one from a classic single peak SR curve, and then the stochastic resonance phenomenon almost disappears.