The Green Function Approach to the Two—Dimensional t—J model

We investigate the two-dimensional t-J model by the Green function approach with the Hubbard operator.The phase diagram,including the Neel temperature and the superconducting transition temperature simultaneously,is derived.The results are consistent with experiments of cuprate compounds.     

Incommensurate Antiferromagnetism in the Extended t－J Model

The effect of the extra second neighbor hopping t‘ on the incommensurate spin correlation in the t-J model in the underdoped regime is studied within the fermion-spin theory.It is shown that although the extra second neighbor hopping t‘ is systematically accompanied with the increasing of the weight of the incommensurate peaks in the dynamical spin structure factor,for the physical reasonable small value of t‘ the qualitative behavior of the incommensurate spin correlation in the t-t‘-J model is the same as in the case of t-J model.     

The Critical Properties of One—Dimensional Extended Hubbard Model

In the framework of nonperturbative quantum field theory,the critical phenomena of one-dimensional extended Hubbard model (EHM) at half-filling are discussed from weak to intermediate interactions.After the EHM being mapped into two decoupled sine-Gordon models,the ground state phase diagram of the system is derived in an explicit way.It is confirmed that the coexisting phases appear in different interaction regimes which cannot be found by conventional theoretical methods.The diagram shows that there are seven different phase regions in the ground state,which seems not to be the same as previous discussions,especially the boundary between the phase separation and condensed phase regions.The phase transition properties of the model between various phase regions are studied in detail.     

The Critical Properties of a Modulated Quantum sine—Gordon Model

A new procedure of trial variational wave functional is proposed for invostigating the mass reuormalizationand the local structure of the ground state of a one-dimensional quantum sine-Gorrdonm model with linear spatial modu-lation, whose ground state differs from that without modulation. Thc phase diagram obtained in parameters (αA 2,β2)plane shows that the vertical part of the boundary between soliton lattice phase and iucommensurate (IC) phase withvanishing gap sticks at β2 = 4, the IC phase can only appear forβ2 ＞ 47r and thc IC phase regime is enlarged withincreasing spatial modulation in the case of definite parameter αA-2. The transition is of the continuous type on thevertical part of the boundary, while it is of the first order on the boundary forβ2 ＞ 47r.     

Exact Solution of an Extended Hubbard Model with Electron—Lattice Interaction for an Organic Ferromagnetic Polymer

Using an exact diagonalization method,we study an extended Hubbard model with an electron-lattice interaction for an organic ferromagnetic chain with radical coupling.The result shows that the ferromagnetic ground state originates from the antiferromagnetic correlation between adjoining sites,which is enhanced by the on-site e-e repulsion.The intersite e-e repulsion induces the inhomogeneous distribution of the charge density.The dimerization is decreased by the e-e interaction and the radical coupling.The electron-lattice interaction and the radical coupling can transfer the spin density and charge density between the main chain and the radicals.     

Influence of Inhomogeneity on Critical Behavior of Earthquake Model on Random Graph

We consider the earthquake model on a random graph. A detailed analysis of the probability distribution of the size of the avalanches will be given. The model with different inhomogeneities is studied in order to compare the critical behavior of different systems. The results indicate that with the increase of the inhomogeneities, the avalanche exponents reduce, i.e., the different numbers of defects cause different critical behaviors of the system. This is virtually ascribed to the dynamical perturbation.     

Critical behaviours and magnetic properties of three-dimensional bond and anisotropy dilution Blume——Capel model in the presence of an applied field

This paper studies the critical behaviours and magnetic properties of three-dimensional bond and anisotropy dilution Blume--Capel model (BCM) in the presence of an applied field within the effective field theory. The trajectory of tricritical point, reentrant transitions and degenerate patterns of anisotropy are obtained both for the bond and the anisotropy dilutions. The global phase diagrams demonstrate unusually reentrant phenomena. The temperature dependences of magnetization curves undergo remarkable spin glass behaviour at low temperatures, and transform from ferromagnetism to paramagnetism at high temperature in applied fields. Temperature dependence of magnetic susceptibility curve is in qualitative agreement with experimental result.     

Calculation of Total Recation Cross Sections Induced by Intermediate Energy α—Particles with the Boltamann—Uehling—Uhlenbeck Model

The Boltzmann-Uehling-Uhlenbeck(BUU)model,which includes the Fermi motion,the mean field,individual nucleon-nucleon(N-N)interactions and the Pauli blocking effect,etc.,is used to cakulate the total reaction cross section σR induced by a-particlea on different targets in the incident energy range from 17.4 to 48.1 MeV/u. The calculation result can well reproduce the experimental data.The nucleus-nucleas interaction radius parameter ro was extracted from experimental σR.It is found ro becomes constant with the increasing mass number of target.     

Information Measure for Size Distribution of Avalanches in the Bak—Sneppen Evolution Model

Information of avalanche size distribution is measured by calculating information entropy(IE) in the BakSneppen evolution model.It is found that the IE increases as the model evolves,Specifically,we establish the relation between the IE and the self-oprganized threshold fc.The variation of the IE near the critical point yields an exponent entropy index E=(τ-1)/σ，where τand σ prepresent the critical exponents for avalanche size distribution and avalanche size cutoff,respectively,A new quantity Dτ(g)(g=1-(fc-G)^τ-1)/σ,where G is the gap of the current state),defined as 1-Iτ(g)/Iτ(1),with Iτ(g) and Iτ(1)being the IE for the current state and the critical one respectively,is suggested that it represents the distance between the state with gap G and the critical one.     

Exact Analytical Solutions to the Two—Mode Mean—Field Model Describing Dynamics of a Split Bose—Einstein Condensate

We present the analytical solutions to the two-mode mean-field model for a split Bose-Einstein condensate.These explicit solutions completely determine the system‘s dynamics under the two-mode mean-field approximation for all possible initial conditions.