International Journal of Modern Physics B

Following the direct observation of abrupt changes in the superconducting ground state in doped low dimensional antiferromagnets, we have identified a phase transition where superconductivity is optimal. The experiments indicate the presence of a putative quantum critical point associated with the emergence of a glassy state. This mechanism is argued to be an intrinsic property and as such, largely independent of material quality and the level of disorder.

Sediment transport in fully developed turbulent open channel flow has been investigated using large eddy simulation (LES) of the incompressible Navier–Stokes equations. The scalar transport equation of the sediments concentration, which is based on the continuous-phase approach, is adopted. The settling process is taken into account with a modified settling velocity appearing in the sediment concentration equation. A Smagorinsky model allowing for the interaction between the fluid flow and the suspended sediment is used to simulate the unresolved, subgrid scale terms. The LES results are compared with the experimental data, and good general agreement is achieved.

We calculate the conductivity of a clean graphene sheet at finite temperatures starting from the tight-binding model. We obtain a finite value for the dc-conductivity at zero temperature. For finite temperature, the spontaneous electron-hole creation, responsible for the finite conductivity at zero temperature, is washed out and the dc-conductivity yields zero. Our results are in agreement with calculations based on the field-theoretical model for graphene.

In the present work, comparative study of the dielectric behavior of Mn_0.4Zn_0.6Fe₂O₄ ferrite synthesized with and without H₂O₂ (hydrogen peroxide) has been presented. The dc resistivity has been improved by the citrate precursor method as compared to the ceramic method, and it is further improved by the addition of H₂O₂, which acts as a strong oxidizing agent. We have shown by means of X-ray diffraction that the resulting ferrite is made up of nanocrystallites and the average size of these nanocrystallites–calculated by Scherrer's formula–depends on the polarizer. The average particle size was found to be ~70 nm with H₂O₂ and ~88 nm without H₂O₂. The particle size is further confirmed by scanning electron microscopy. Both the results are found to be in good agreement. The decrease in dielectric constant and dielectric loss factor by addition of oxidizing agent is justified by inverse proportionality between the resistivity and dielectric constant. Possible mechanisms contributing to these processes have been discussed.

The damage spreading of the Ising model on the homo- and hetero-cell lattices (here the topological hexagonal lattice and the 4–8 lattice) with competing Glauber (G-) and Kawasaki (K-) dynamics is studied and the results are compared. For the homo-cell lattice, we pay attention to the pure K-dynamics or the cases in which the K-dynamics is dominant. We get four main conclusions related to the K-dynamics through our calculations: (1) the damage always spreads as long as Kawasaki dynamics is dominant during the competition of two dynamics; (2) the relation for the saturation damage, 〈s〉_∞ = 0.5, holds for K-dynamics whatever the updating rules are; (3) 〈s〉_∞ = 0.5 is independent of the structures of the system; (4) the DS process under pure K-dynamics converges very slowly, especially for T = 0 K-dynamics. For the hetero-cell lattice, we are interested in the long-range interaction between spins and the different interaction strength for the spins in the hetero-cells. To include the long-range spin interaction, we consider the spin interactions up to next-nearest neighbors. It is shown that the inclusion of the next-nearest-neighbor interaction enhances the transition temperature greatly. The explanation and discussion for the results are presented.

Macroscopic derivation of the entrainment in a supersolid cylinder induced by a surface elastic wave (of small amplitude) propagating along the flexible interface is conducted by considering the nonlinear coupling between the interface and the rarefaction effect. We obtain the critical bounds for zero-volume-flow-rate states corresponding to specific rarefaction measure and wave number which is relevant to the rather small critical velocity or disappearance of supersolid flows reported by Kim and Chan or Rittner and Reppy.

We study nonclassic solitonic structures on the modified oscillator — chain proposed by Peyrard and Bishop to model DNA. The two DNA's strands are linked together by hydrogen bonds that are modeled by the Morse potential. This Peyrard–Bishop model with inharmonic potential in the optical part of the Hamiltonian gives rise to several nonclassical solutions, i.e., compact-cusp and anti-peak or crowd like soliton solutions. These structures could represent not only local openings of base pairs, but also the inverse process that heals the formation of broken hydrogen bonds.

Knowledge of distribution coefficient values is essential in estimating the refining efficiency, and plays an important role during the purification process, typically zone refining. The effective distribution coefficient "K_eff" of impurities Se, Fe, Cr and Pb in tellurium was determined in the present study and found to be 0.48, 0.05, 0.25 and 0.19, respectively. The results are validated by comparing with the available published data, and we observed a difference of less than one order, which was reasonably comparable. The influence of "K_eff" on zone refining efficiency was examined and it was noticed that the effective distribution coefficient increases with respect to the translation rate, which is minimum at an optimum lower translation rate (= 30 mm/h). The relative solute concentration C/C₀ is determined experimentally, which shows the best fit of experimental values with Pfann's equation. The impurity profile along the length of the zone refined ingot is also discussed.

We have calculated the orbital correlation of the spinless two orbitals Hubbard chain in the limit of a very strong on-site Coulomb interaction and half-filling. The Hamiltonian is written in the form of pseudospin operators, and the Hilbert space is restricted to those states with only one electron per lattice site. The ground state wave function has been calculated using the density matrix renormalization group method. It has been found that the orbital correlations occur in the chain along the x-, y-, and z-axis and these are in antiferro-orbital states.

Here, a new approach for calculating the triggering drain bias at the onset of the kink effect, kink voltage, V_kink, for PD SOI NMOS devices utilizing electron drift properties in the channel is given. This approach directly relates electron mobility in the channel to the kink effect and enables one to determine kink voltage knowing the device technology. It also gives the possibility for calculating mobility from the kink voltage. Theory is compared to the previously published experimental results and based on this match, the behavior of the kink voltage for PD SOI NMOS components for various technology parameters is predicted. Explanation for the appearance of the kink in the volt regime below the band gap of silicon is also given. From this consideration, design rules for PD SOI NMOS devices are derived in order to soothe the kink effect.

The binding energy of a bound polaron in an anisotropic quantum dot (QD) subject to electric and magnetic fields along the growth axis has been investigated by using a variational method of Pekar type, taking into account the electron-bulk LO-phonon interaction. The results show that the binding energy decreases with increasing electric field strength and increases with increasing confinement strengths in the lateral and the longitudinal direction, the magnetic field strength, and the Coulomb potential.