Extended Bose-Hubbard model with pair hopping on triangular lattice

We study systematically an extended Bose-Hubbard model on the triangular lattice by means of a meanfield method based on the Gutzwiller ansatz. Pair hopping terms are explicitly included and a three-body constraint is applied. The zero-temperature phase diagram and a variety of quantum phase transitions are investigated in great detail. In particular, we show the existence and the stability of the pair supersolid phase.     

Universal critical properties of the Eulerian bond-cubic model

We investigate the Eulerian bond-cubic model on the square lattice by means of Monte Carlo simulations,using an efficient cluster algorithm and a finite-size scaling analysis.The critical points and four critical exponents of the model are determined for several values of n.Two of the exponents are fractal dimensions,which are obtained numerically for the first time.Our results are consistent with the Coulomb gas predictions for the critical O(n) branch for n < 2 and the results obtained by previous transfer matrix calculations.For n=2,we find that the thermal exponent,the magnetic exponent and the fractal dimension of the largest critical Eulerian bond component are different from those of the critical O(2) loop model.These results confirm that the cubic anisotropy is marginal at n=2 but irrelevant for n < 2.     

Cd_(0.96)Zn_(0.04)S/Cd_(0.97)Mn_(0.03)S/Cd_(0.96)Zn_(0.04)S多层纳米线中s-d交换作用的研究

以氧化铝纳米孔为模板,采用直流电化学沉积的方法制备了Cd_(0.96)Zn_(0.04)S/Cd_(0.97)Mn_(0.03)S/Cd_(0.96)Zn_(0.04)S量子阱纳米线阵列,并系统研究了该纳米线阵列在不同温度和不同磁场下的电学输运特性.随着外磁场的变化,样品表现出共振传输特性.通过量子阱理论对实验现象进行了分析,直接得到了稀磁层Cd_(0.97)Mn_(0.03)S中s-d交换作用常数N_0α的定量结果.研究发现该交换作用常数随温度具有e~(-1/T)的变化趋势.     

Skyrmion crystals in pseudo-spin-1/2 Bose–Einstein condensates

Exact two-dimensional solutions are constructed for the pseudo-spin-1/2 Bose–Einstein condensates,which are described by the coupled nonlinear Gross–Pitaevskii equations where the intra-and inter-species coupling constants are assumed to be equal.The equations are decoupled by means of re-combinations of the nonlinear terms of the hyperfine states according to the spatial dimensions.The stationary solutions form various spin textures which are identified as skyrmion crystals.In a special case,a crystal of skyrmion–anti-skyrmion pairs is formed in the soliton limit.     

PHASE TRANSITION IN A NONEQUILIBRIUM POTTS MODEL WITH COMPETING DYNAMICS: A MONTE-CARLO STUDY

The nonequilibrium steady state of three-state Potts model evolving under combined Glauber dynamics at temperature β^-1 and Kawasaki dynamics at β′= 0 is studied by Monte-Carlo simulations. As the exchange rate p increases, the phase transition changes from second to first order. The critical exponents of second-order transition are independent of p, and the critical properties for different p belong to the same universality class.     

Typicality at quantum-critical points

We discuss the concept of typicality of quantum states at quantum-critical points, using projector Monte Carlo simulations of an S = 1/2 bilayer Heisenberg antiferromagnet as an illustration. With the projection(imaginary) time τ scaled as τ = a Lz, L being the system length and z the dynamic critical exponent(which takes the value z = 1 in the bilayer model studied here), a critical point can be identified which asymptotically flows to the correct location and universality class with increasing L, independently of the prefactor a and the initial state. Varying the proportionality factor a and the initial state only changes the cross-over behavior into the asymptotic large-L behavior. In some cases, choosing an optimal factor a may also lead to the vanishing of the leading finite-size corrections. The observation of typicality can be used to speed up simulations of quantum criticality, not only within the Monte Carlo approach but also with other numerical methods where imaginary-time evolution is employed, e.g., tensor network states, as it is not necessary to evolve fully to the ground state but only for sufficiently long times to reach the typicality regime.