7 research outputs found
Phase diagram of S=1/2 two-leg XXZ spin ladder systems
We investigate the ground state phase diagram of the S=1/2 two-leg spin
ladder system with an isotropic interchain coupling. In this model, there is
the Berezinskii-Kosterlitz-Thouless transition which occurs at the XY-Haldane
and the XY-rung singlet phase boundaries. It was difficult to determine the
transition line using traditional methods. We overcome this difficulty using
the level spectroscopy method combined with the twisted boundary condition
method, and we check the consistency. We find out that the phase boundary
between XY phase and Haldane phase lies on the line. And we show
that there exist two different XY phases, which we can distinguish
investigating a correlation function
Staggered dimer order in S=1/2 quantum spin ladder system with four spin exchange
We study the S=1/2 quantum spin ladder system with the four-spin exchange,
using density matrix renormalization group method and an exact diagonalization
method. Recently, the phase transition in this system and its universality
class are studied. But there remain controversies whether the phase transition
is second order type or the other type and the nature of order parameter. There
are arguments that the massless phase appears. But this does not agree with our
previous result. Analyzing DMRG data, we try a new approach in order to
determine a phase which appears after the phase transition. We find that the
edge state appears in the open boundary condition, investigating excitation
energies of states with higher magnetizations.Comment: Submitted to Phys. Rev. B, (REVTeX4
Universality class of S=1/2 quantum spin ladder system with the four spin exchange
We study s=1/2 Heisenberg spin ladder with the four spin exchange. Combining
numerical results with the conformal field theory(CFT), we find a phase
transition with central charge c=3/2. Since this system has an SU(2) symmetry,
we can conclude that this critical theory is described by k=2 SU(2)
Wess-Zumino-Witten model with Z symmetry breaking