Ground state phase diagram of an two-leg Heisenberg spin ladder system with negative four-spin interaction

Hijii, Keigo; Sakai, Toru

We investigate the ground-state phase diagram and critical properties of the two-leg Heisenberg spin ladder system with a negative four-spin interaction. We numerically determine a phase boundary between the rung singlet phase and the columnar dimer (CD) phase by the phenomenological renormalization group method, and one between the CD phase and the Haldane phase by the twisted boundary condition method. We confirm that the phase transition between the CD phase and the Haldane phase is of second order and this universality class is described by the = 2 (2) Wess-Zumino-Novikov-Witten nonlinear model, calculating the central charge and scaling dimensions.