International Journal of Modern Physics B

The one-dimensional interacting topological insulator is studied by means of exact diagonalization method. The topological properties are examined with the existence of the edge states and the quantized berry phase at half-filling. It is found that the topological phases are not only robust to small repulsive interactions but also are stabilized by small attractive interactions and also finite repulsive interaction can drive a topological nontrivial phase into a trivial one while the attractive interaction can drive a trivial phase into a nontrivial one. These results could be realized experimentally using cold atoms trapped in the 1D optical lattice.

Recently, a concept of orthogonal metal has been introduced to reinterpret the disordered state of slave-spin representation in the Hubbard model as an exotic gapped metallic state. We have extended this concept to study the slave-spin representation of Hubbard model on the honeycomb lattice. It is found that a novel gapped metallic state coined orthogonal Dirac semimetal is identified. Such state corresponds to the disordered phase of slave-spin and has the same thermal-dynamical and transport properties as Dirac semimetal but its singe-particle excitation is gapped.

We studied theoretically the spin-dependent electron transport properties of a three-terminal nanostructure proposed by Xiao and Chen [J. Appl. Phys.1, 108 (2010)]. The spin-resolved recursive Green's function method is used to calculate the three-terminal spin-polarization. We focus on the influence both of the structural parameters and Rashba spin–orbit coupling (SOC) strength in the investigated system. It is shown that the spin-polarization is still a reasonable value for being observable in experiment with small Rashba SOC strength and longer length of the wide region in the investigated system. The underlying physics is revealed to originate from the effect of SOC-induced effective magnetic field at the structure-induced Fano resonance. This length of the middle wide region in three-terminal nanostructure can be more easily fabricated experimentally.

We numerically study the thermoelectric transport properties in trilayer graphene in the presence of a strong perpendicular magnetic field and disorder. In the unbiased case, we find that the thermoelectric transport has similar properties as in monolayer graphene. In the high temperature regime, the transverse thermoelectric conductivity α_xy saturates to a universal value 8.31 k_Be/h at the center of each Landau level (LL), and displays a linear temperature dependence at low temperatures. The Nernst signal has a peak at the central LL with a height of the order of k_B/e, while the thermopower changes sign. We attribute this to the coexistence of particle and hole LLs around the Dirac point. When a finite interlayer bias is applied and a band gap is opened, it is found that the transport properties are consistent with those of a band insulator.

The transport property of electrons in a mesoscopic ring with one arm subject to gate is investigated through the quantum waveguide theory. The persistent current is produced and controlled by tuning the strength of potential energy even in the absence of magnetic field. The persistent current can not only be observed if one tunes the Fermi energy nearing the antiresonance or the Fano resonance of the transport current in the weak strength of potential energy, but also can be detected at the resonance of the transport current in the strong strength of potential energy. An impurity is embedded in the right lead of the ring was also investigated and the large persistent current can be produced by varying the strength of the impurity potential and the length between the impurity and ring.

A two-dimensional numerical modeling has been developed to analyze the dynamic evolution of heat transfer in a cylindrical composite conductor Cu/NbTi. The model solves the transient heat equation coupled with current shift in NbTi and copper. The minimum quench energy and quench propagation velocity are calculated and analyzed, these numerical results yield the experiment results. The effect of different cross-section ratio of copper to superconductor on the electric field produced by heat disturbance is discussed.

Within the framework of quantum field theory, we find that uniform Bose atomic gases with noncontact interaction can undergo a Bardeen–Cooper–Schrieffer (BCS) condensation below a critical temperature. In the BCS condensation state, bare atoms with opposite wave vectors are bound into pairs, and unpaired bare atoms are transformed into a new kind of quasi-particle, i.e., the dressed atom. The atom-pair system is a condensate or a superfluid and the dressed-atom system is a normal fluid. At absolute zero temperature the condensate possesses a lowest negative energy. The critical temperature and the effective mass of dressed atoms are derived analytically. The transition from the BCS condensation state to the normal state is a first-order phase transition.

A continuum hydrodynamic model is presented for one-component liquid–gas flows on nonisothermal solid substrates. Numerical simulations are carried out for evaporative droplets moving on substrates with thermal gradients. For droplets in one-component fluids on heated/cooled substrates, the free liquid–gas interfaces are nearly isothermal. Consequently, a thermal singularity occurs at the contact line while the Marangoni effect due to interfacial temperature variation is suppressed. Through evaporation/condensation near the contact line, the thermal singularity makes the contact angle increase with the increasing substrate temperature. Due to this effect, droplets will move toward the cold end on substrates with thermal gradients. The droplet migration velocity is found to be proportional to the change of substrate temperature across the droplet. It follows that for two droplets of different sizes on a substrate with temperature gradient, the larger droplet moves faster and will catch up with the smaller droplet ahead. As soon as they touch, they coalesce rapidly into an even larger droplet that will move even faster.

We examine several widely used statistical field theoretic methods in theoretical polymer physics. A systematic derivation for the polymer field theoretic model is given within the framework of the effective Landau theory. After constructing the field theoretic model, we perform a perturbative expansion of the model, and then the mean-field approximation and the Gaussian fluctuation approximation are introduced into the treatment of the model in order. We also outline a derivation for the self-consistent Hartree theory in polymer physics within a variational scheme. The applications of these methods are also discussed accordingly.

The anisotropic characters of simple cubic lattice are investigated in this paper. Both the linear and nonlinear wave propagating in this lattice have been studied. The dispersion relation has been studied numerically. It is shown that the dispersion relation strongly depends on the directions of wave propagation. Generally, the direction of waves has the inclination angle α with respect to particle displacement. There are compressional waves α = 0 or transverse waves α = π/2 only for some special cases. The nonlinear waves in this lattice have also been studied. The anisotropic characters of this lattice for the nonlinear waves have also been shown. The compressional and transverse nonlinear solitons have also been studied. The characters of both solitons, such as amplitude and width, have been investigated.

The statistical mechanics of collisionless self-gravitating systems is a longstanding puzzle, which has not yet been successfully solved. We performed preliminary investigations and then formulated a framework of the entropy-based equilibrium statistical mechanics for collisionless self-gravitating systems. This theory is based on the Boltzmann–Gibbs entropy and includes the generalized virial equations as additional constraints. With the truncated distribution function to the lowest order, we derived a set of second-order equations for the equilibrium states of the system, and solved the numerical solutions of these equations. It is found that there are three types of solutions for these equations. Both the isothermal and divergent solutions are thermally unstable and have unconfined density profiles with infinite mass, energy and spatial extent. The convergent solutions, however, seem to be reasonable. These solutions are just the lowest-order approximation, but they have already manifested the qualitative success of our theory. The second-order variations of the entropy functional indicate that the stationary solutions are neither maximum nor minimum, but saddle-point solutions. Inspired by the saddle-point solutions, we distinguish between two types of perturbations in self-gravitating systems, namely, the large-scale mass perturbation and the small-scale density perturbation, which correspond to long-range violent relaxation and short-range relaxation/Landau damping, respectively, which operate in different fashions. This result is consistent with Antonov's proof, or Binney's argument, that there are no global maximum entropy states for self-gravitating systems. These investigations indicate the achievements that we have made towards this long-standing unsolved problem on the statistical mechanics of self-gravitating systems.