Modern Physics Letters B

Within the Luttinger Hamiltonian, electric-field-induced resonant spin polarization of a two-dimensional hole gas in a perpendicular magnetic field was studied. The spin polarization arising from splitting between the light and the heavy hole bands shows a resonant peak at a certain magnetic field. Especially, the competition between the Luttinger term and the structural inversion asymmetry leads to a rich resonant peaks structure, and the required magnetic field for the resonance may be effectively reduced by enlarging the effective width of the quantum well. Furthermore, the Zeeman splitting tends to move the resonant spin polarization to a relative high magnetic field and destroy these rich resonant spin phenomena. Finally, both the height and the weight of the resonant peak increase as the temperature decreases. It is believed that such resonant spin phenomena may be verified in the sample of a two-dimensional hole gas, and it may provide an efficient way to control spin polarization by an external electric field.

We review the momentum-jump approximation in the quantum-classical Liouville formulation of nonadiabatic dynamics. We consider different momentum shift rules and study their numerical importance in computer simulations of the spin-boson model. Our findings might help the design of generalized sampling schemes of nonadiabatic dynamics at long time.

The magnetization and the specific heat of two single molecule magnets (SMM) with spin-10, Mn₁₂-ac and Fe₈, are compared for Dβ ~ 0.031. The rhombic term in the Fe₈ molecule makes the x-component of its magnetization to be larger than that of the Mn₁₂-ac molecule. The axial symmetry of the Mn₁₂-ac favors the z-component of its magnetization, in comparison to the Fe₈ molecule. For T ≳ 18 K, the specific heat of the Mn₁₂-ac is large (80%, at most) than that of the Fe₈, at the same temperature. The corrections from the S = 9 excited states of these SMM's do not invalidate our results. An unexpected result occurs when the angle between the easy-axis and the external magnetic field equals π/4: the aforementioned percentage difference of the specific heat reaches 3% for D β ≲ 0.025 and h/k ∈[1.93, 2.04], when they are compared at distinct temperatures . This small percentage difference also happens for the average specific heat of both SMM's at those temperatures and h/D_Mn ∈ [1.97, 2.1].

Nominally undoped AlGaN/GaN heterostructure samples were grown on c-plane sapphire substrates by low-pressure metal-organic chemical vapor deposition, and their material properties, such as crystal quality, roughness of heterointerface, thickness and Al mole fraction of AlGaN barrier layer, were identified by high resolution X-ray diffraction (HRXRD). Mercury-probe capacitance–voltage (C–V) measurements were carried out to investigate the carrier distribution in the heterostructures and accurately evaluate the sheet carrier concentration of two-dimensional electron gas (2DEG) formed at AlGaN/GaN heterointerface. The dependence of C–V characteristics of these samples on some key material parameters were clearly revealed. The Al-content effect, barrier-thickness effect in AlGaN layer, and their synergy effect were specifically studied. It demonstrated that the C–V characteristics of AlGaN/GaN heterostructure could be improved by perfecting the crystal epitaxial process, and adjusting the Al-content or thickness of AlGaN barrier layer.

We have proposed and investigated a model of drying colloidal suspension drop placed onto a horizontal substrate in which the sol to gel phase transition occurs. The temporal evolution of volume fraction of the solute and the gel phase dynamics were obtained from numerical simulations. Our model takes into account the fact that some physical quantities are dependent on volume fraction of the colloidal particles.

The impurity binding energy in a polar rectangular quantum wire is studied by a variational approach. The electron- and ion-longitudinal-optical-phonon interactions are both taken into account in the calculations. The numerical results for GaAs quantum wire indicate that the phonon effects reduce obviously the binding energy and cannot been neglected. The ion-phonon coupling is dominant in various phonon effects. The phonon contribution is sensitive to the size and shape of the quantum wire section.

The pyroelectric and phase transition properties of a finite alternating ferroelectric superlattice with three surface layers are studied on the basis of the transverse Ising model by using the mean field approximation. The temperature-dependence of the polarization and pyroelectric coefficient of the superlattice with various inter-layer exchange interaction constants are given. The profiles of the polarization as well as the pyroelectric coefficient of the superlattice are shown. By taking into account the effects of the exchange interaction and transverse field parameters on the phase diagrams, we find that the phase transition properties of the superlattice are sensitive to the changes of transverse Ising model parameters.

Density functional calculations were performed to investigate the properties of a combination of two representative carbon nanotubes by assistance of the atomic sites of uracil, which is the characteristic nucleobase of RNA. The obtained parameters indicated that the resulting compound exhibit new properties with respect to the original nanotubes and uracil. The effects of the modification process were significant for the dipole moments and conductivity properties of the components as were seen by the significant changes in the new compound. The values of quadrupole coupling constants for the nitrogen and oxygen atoms of the uracil counterpart of the investigated models also indicated the effects of changes of the electronic environments of the components due to the modification process.