6,512 research outputs found
Quantum phase transitions in the J-J' Heisenberg and XY spin-1/2 antiferromagnets on square lattice: Finite-size scaling analysis
Full text linkWe investigate the critical parameters of an order-disorder quantum phase
transitions in the spin-1/2 Heisenberg and XY antiferromagnets on square
lattice. Basing on the excitation gaps calculated by exact diagonalization
technique for systems up to 32 spins and finite-size scaling analysis we
estimate the critical couplings and exponents of the correlation length for
both models. Our analysis confirms the universal critical behavior of these
quantum phase transitions: They belong to 3D O(3) and 3D O(2) universality
classes, respectively.Comment: 7 pages, 3 figure
Numerical Studies of the two-leg Hubbard ladder
Full text linkThe Hubbard model on a two-leg ladder structure has been studied by a
combination of series expansions at T=0 and the density-matrix renormalization
group. We report results for the ground state energy and spin-gap
at half-filling, as well as dispersion curves for one and two-hole
excitations. For small both and show a dramatic drop near
, which becomes more gradual for larger . This
represents a crossover from a "band insulator" phase to a strongly correlated
spin liquid. The lowest-lying two-hole state rapidly becomes strongly bound as
increases, indicating the possibility that phase separation may
occur. The various features are collected in a "phase diagram" for the model.Comment: 10 figures, revte
Critical and off-critical studies of the Baxter-Wu model with general toroidal boundary conditions
Full text linkThe operator content of the Baxter-Wu model with general toroidal boundary
conditions is calculated analytically and numerically. These calculations were
done by relating the partition function of the model with the generating
function of a site-colouring problem in a hexagonal lattice. Extending the
original Bethe-ansatz solution of the related colouring problem we are able to
calculate the eigenspectra of both models by solving the associated
Bethe-ansatz equations. We have also calculated, by exploring the conformal
invariance at the critical point, the mass ratios of the underlying massive
theory governing the Baxter-Wu model in the vicinity of its critical point.Comment: 32 pages latex, to appear in J. Phys. A: Math. Ge
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