Modern Physics Letters B

We propose a scheme to simulate the t–J–U model and investigate the quantum phase transitions using cold atoms confined in a two-dimensional optical lattice. By adjusting the parameters of external laser fields, we find a phase transition from antiferromagnetic phase to Gossamer superfluid. The Gossamer superfluid has a d-wave or mixed d- and s-wave symmetry, depending on the hopping parameters which can be adjusted by tuning the laser field. Experimental protocol to observe these new phenomena for future experiments has also been briefly discussed.

Based on the invariant eigen-operator method³ we developed a general way to calculate the energy gaps of quadratic Boson or Fermion Hamiltonians. As an application, we calculated the energy gaps of an electron in uniform magnetic field (UMF) and a quadratic potential. We also checked the gauge invariance of electromagnetic field.

The superconducting gap ratio R = 2Δ(0)/k_BT_c has been studied in the context when the Fermi level is close to the van Hove singularity. In this approach, we consider the interaction is related to the phonons at low temperature but at high temperature, it is relevant to the magnetic excitations. Our results show that the superconducting gap ratio R takes large values in qualitative agreement with experimental data.

The shapes of DNA, carbon nanotube (CNT) and vesicle are determined by the minimum of their elastic energy. Two central results about the low-dimensional elastic structure are reported here. Firstly, if the energy density of a one-dimensional structure is only related to its curvature, we generally find that a helix solution with the helix angle θ = ±π/4 will have zero total energy. Secondly, with the fixed length and radii, the helical multi-walled carbon nanotubes (MWNTs) and DNA will have the lowest energy when the helix angle θ = ±π/3.

The binding energy of a hydrogenic donor impurity in a zinc-blende GaN/AlGaN cylindrical quantum well wire (QWW) is calculated in the framework of effective-mass envelope-function theory using the plane wave basis. It is shown that the donor binding energy is highly dependent on the impurity position, the radius of the wire and the external electric field. In addition, Stark shift dependence on the radius of the QWW and the external electric field is also calculated. The donor binding energy has a maximum when the impurity is located at the center of the QWW. The donor binding energy decreases with the increase of the external electric field, but stark shift increases with the increase of the external electric field or the radius of the QWW.

In this paper, on the basis of Huybrechs' strong-coupled polaron model, Tokuda modified linear-combination operator and the unitary transformation methods are used to study the properties of the strong-coupled polaron considering the influence of Rashba effect, which is brought by the spin-orbit (SO) interaction, in the asymmetric quantum dot (QD). The expressions of the effective mass as a function of the transverse and longitudinal confinement strengths, the velocity and the vibration frequency were derived. Numerical calculation on the RbCl QD, as an example, is performed and the results show that the total effective mass of the polaron is composed of three parts. The interaction between the orbit and the spin with different directions has different effects on the effective mass of the polaron.

Based on the model of the single TEM₀₀ Gaussian beam optical tweezers, the transverse and longitudinal optical trapping forces of micro-particles are calculated by ray-optics theory. The similarities and differences of the longitudinal optical trap shapes, which are computed by two different methods, are analyzed. We studied the relation between the optical trap stiffness and the particle parameters which include the size and refractive index (RI), and found that the ratio of the transverse and longitudinal stiffness is a constant when the refractive indices of the particles are the same. Through the analysis, the results show that there is an important relationship between the optical stiffness and the product of particle RI and radius. With this relationship, we can obtain the particle RI by measuring the optical stiffness and the particle radius. This novel micro-particle RI measurement method is of great usefulness in atmospheric environmental science, polymer chemistry science, identification of mineral science and bio-medical science.